Instrument and method for milling a path into bone

ABSTRACT

An instrument and method for cutting a path in bone are provided. The instrument includes a curved guide member defining a curved opening extending therein, and a bit member positioned within the opening of the guide member. The bit member is adapted to move within the opening of the guide member to cut a path in bone.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/446,963 filed on Feb. 12, 2003. U.S. ProvisionalApplication No. 60/446,963 is herein incorporated by reference for alllegitimate purposes.

BACKGROUND

[0002] The present disclosure relates generally to the field oforthopedics and spinal surgery, and in some embodiments, the presentdisclosure relates to intervertebral prosthetic joints for use in thetotal or partial replacement of a natural intervertebral disc, andmethods and tools for use therewith.

[0003] In the treatment of diseases, injuries or malformations affectingspinal motion segments, and especially those affecting disc tissue, ithas long been known to remove some or all of a degenerated, ruptured orotherwise failing disc. In cases involving intervertebral disc tissuethat has been removed or is otherwise absent from a spinal motionsegment, corrective measures are taken to ensure the proper spacing ofthe vertebrae formerly separated by the removed disc tissue.

[0004] In some instances, the two adjacent vertebrae are fused togetherusing transplanted bone tissue, an artificial fusion component, or othercompositions or devices. Spinal fusion procedures, however, have raisedconcerns in the medical community that the bio-mechanical rigidity ofintervertebral fusion may predispose neighboring spinal motion segmentsto rapid deterioration. More specifically, unlike a naturalintervertebral disc, spinal fusion prevents the fused vertebrae frompivoting and rotating with respect to one another. Such lack of mobilitytends to increase stresses on adjacent spinal motion segments.

[0005] Additionally, several conditions may develop within adjacentspinal motion segments, including disc degeneration, disc herniation,instability, spinal stenosis, spondylosis and facet joint arthritis.Consequently, many patients may require additional disc removal and/oranother type of surgical procedure as a result of spinal fusion.Alternatives to spinal fusion are therefore desirable.

[0006] In particular, this disclosure relates to an instrument that aidsin the insertion of alternatives to spinal fusion.

SUMMARY

[0007] An instrument for cutting a path in bone is provided. Theinstrument includes a curved guide member defining a curved openingextending therein, and a bit member positioned within the opening of theguide member. The bit member is adapted to move within the opening ofthe guide member to cut a path in bone.

[0008] In another embodiment, an instrument for cutting a path in boneis provided. The instrument includes a curved guide member defining acurved opening extending therein, a bit member positioned within theopening of the guide member, a rotatable element operatively connectedto the bit member to impart rotational movement to the bit member, and ahandle operatively connected to the bit member to impart translationalmovement to the bit member. The bit member is adapted to cut a curvedpath into bone via rotational movement in and translational movementthrough the guide member.

[0009] In yet another embodiment, a method for cutting a curved pathinto bone is provided. The method includes providing an instrumenthaving a curved guide member, the curved guide member defining a curvedopening therein, positioning a bit member within the opening of theguide member, actuating the instrument to impart rotational movement tothe bit member, engaging the bit member with bone, and imparting atranslational force to the bit member to cut a curved path in bone.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a lateral view of a portion of a spondylosed vertebralcolumn.

[0011]FIG. 2 is a lateral view of a pair of adjacent vertebral endplatesof FIG. 1.

[0012]FIG. 3a is a lateral view of the pair of adjacent vertebralendplates of FIG. 2 with a rod and screw arrangement.

[0013]FIG. 3b is a longitudinal, partial sectional view of the pair ofadjacent vertebral bodies of FIG. 3a.

[0014]FIG. 4a is an isometric view of an articulating prosthetic jointfor lateral insertion according to one embodiment of the presentdisclosure.

[0015]FIG. 4b is an isometric view of an articulating prosthetic jointfor lateral insertion according to another embodiment of the presentdisclosure.

[0016]FIG. 4c is a front view of the articulating prosthetic joint forlateral insertion of FIG. 4b.

[0017]FIG. 5 is a longitudinal view of the prosthetic joint of FIG. 4a.

[0018]FIG. 6 is a lateral view of the prosthetic joint of FIG. 4a.

[0019]FIG. 7 is a lateral, partial sectional view of the prostheticjoint of FIG. 4a disposed between a pair of spondylosed vertebralendplates.

[0020]FIG. 8 is a lateral, partial sectional view of an alternativearticulating prosthetic joint disposed between a pair of vertebralendplates.

[0021]FIG. 9 is an isometric view of an alternative articulatingprosthetic joint according to another embodiment of the presentdisclosure.

[0022]FIG. 10 is a lateral, partial sectional view of the prostheticjoint of FIG. 9 disposed between a pair of spondylosed vertebralendplates.

[0023]FIG. 1I is a lateral, partial sectional view of an alternativearticulating prosthetic joint disposed between a pair of vertebralendplates.

[0024]FIG. 12 is an isometric view of a disc prosthesis according toanother embodiment of the present disclosure.

[0025]FIG. 13 is an isometric view of an alternative disc prosthesisaccording to another embodiment of the present disclosure.

[0026]FIG. 14 is an isometric view of an alternative articulatingprosthetic joint for anterior insertion according to another embodimentof the present disclosure.

[0027]FIG. 15 is a longitudinal view of the prosthetic joint of FIG. 14.

[0028]FIG. 16 is a lateral view of the prosthetic joint of FIG. 14.

[0029]FIG. 17 is a lateral view of the prosthetic joint of FIG. 14disposed between a pair of spondylosed vertebral endplates.

[0030]FIG. 18 is a longitudinal view of an alternative articulatingprosthetic joint for anterior insertion according to another embodimentof the present disclosure.

[0031]FIG. 19 is a longitudinal view of an alternative articulatingprosthetic joint for anterior insertion according to yet anotherembodiment of the present disclosure.

[0032]FIG. 20 is a longitudinal view of an alternative articulatingprosthetic joint for anterior insertion according to yet anotherembodiment of the present disclosure.

[0033]FIG. 21 is a longitudinal view of a pair of verterbral endplateshaving slots for receiving the prosthetic joint of FIG. 18.

[0034]FIG. 22 is a longitudinal view of a pair of verterbral endplateshaving slots for receiving the prosthetic joint of FIG. 19.

[0035]FIG. 23 is a longitudinal view of a pair of verterbral endplateshaving slots for receiving the prosthetic joint of FIG. 20.

[0036]FIG. 24 is a lateral, partial sectional view of the prostheticjoint of FIG. 14 disposed between a pair of spondylosed vertebralendplates and an orthopedic implant.

[0037]FIG. 25 is a lateral, partial sectional view of the prostheticjoint of FIG. 14 disposed between a pair of spondylosed vertebralendplates and a lag screw.

[0038]FIG. 26 is a schematic top view of the arrangement depicted inFIG. 25.

[0039]FIG. 27 is a schematic top view of a vertebral body depicting apath for transforaminal insertion.

[0040]FIG. 28 is an isometric view of an alternative articulatingprosthetic joint for transforaminal insertion according to anotherembodiment of the present disclosure.

[0041]FIG. 29 is a lateral view of the prosthetic joint of FIG. 28.

[0042]FIG. 30 is a longitudinal view of the prosthetic joint of FIG. 28.

[0043]FIG. 31a is a lateral, partial sectional view of the prostheticjoint of FIG. 28 disposed between a pair of vertebral endplates.

[0044]FIG. 31b is a longitudinal, partial sectional view of theprosthetic joint of FIG. 28 disposed between a pair of vertebralendplates.

[0045]FIG. 32 is a schematic top view depicting a transforaminal slotformed in a vertebral endplate.

[0046]FIG. 33 is a schematic top view depicting a milling apparatusshown inserted above a vertebral endplate.

[0047]FIG. 34a is a lateral view of the milling apparatus of FIG. 33shown disposed between a pair of adjacent vertebral endplates.

[0048]FIG. 34b is a detailed view of a milling tool of the millingapparatus of FIG. 34a.

[0049]FIG. 34c is a detailed view of an alternative milling tool.

[0050]FIG. 35 is a schematic view of the milling apparatus of FIG. 33.

[0051]FIG. 36 is an isometric view of an alternative articulatingprosthetic joint for transforaminal insertion according to anotherembodiment of the present disclosure.

[0052]FIG. 37 is a lateral view of the prosthetic joint of FIG. 36.

[0053]FIG. 38 is a longitudinal view of the prosthetic joint FIG. 36.

[0054]FIG. 39 is an isometric view of an alternative articulatingprosthetic joint for anterior-oblique insertion according to anotherembodiment of the present disclosure.

[0055]FIG. 40 is a longitudinal view of the prosthetic joint of FIG. 39.

[0056]FIG. 41 is a lateral view of the prosthetic joint of FIG. 39.

[0057]FIG. 42 is lateral, partial sectional view of the prosthetic jointof FIG. 39 disposed between a pair of vertebral endplates.

[0058]FIG. 43 is a longitudinal, partial sectional view of theprosthetic joint of FIG. 39 disposed between a pair of vertebralendplates.

[0059]FIG. 44a is a top, schematic view depicting a slot formed in avertebral endplate for receiving the prosthetic joint of FIG. 39.

[0060]FIG. 44b is a schematic view depicting an alignment processassociated with the insertion of the prosthetic joint of FIG. 39.

[0061]FIG. 45 is an exploded view an alternative prosthetic jointaccording to yet another embodiment of the present disclosure.

[0062]FIG. 46 is an isometric view of the prosthetic joint of FIG. 45.

[0063]FIG. 47 is a longitudinal view of the prosthetic joint of FIG. 46.

[0064]FIG. 48 is a longitudinal view of a pair of adjacent vertebralendplates.

[0065]FIG. 49a is a plan view of an articular component of theprosthetic joint of FIG. 45.

[0066]FIG. 49b is a sectional view of the articular component of FIG.49a taken along the line 49 b-49 b.

[0067]FIG. 50a is a plan view of a modular projection member of theprosthetic joint of FIG. 45.

[0068]FIG. 50b is a sectional view of the modular projection member ofFIG. 50a taken along the line 50 b-50 b.

[0069]FIG. 51 is a plan view of the modular projection member of FIG.50a inserted into the articular component of FIG. 49a.

[0070]FIG. 52 is a plan view of the modular projection member of FIG.50a inserted into the articular component of FIG. 49a depicting themodular projection member in a different position relative to FIG. 51.

DESCRIPTION

[0071] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodiments, orexamples, illustrated in the drawings and specific language will be usedto describe the same. It will nevertheless be understood that nolimitation of the scope of the invention is thereby intended. Anyalterations and further modifications in the described embodiments, andany further applications of the principles of the invention as describedherein are contemplated as would normally occur to one skilled in theart to which the invention relates. As such, individual features ofseparately described embodiments can be combined to form additionalembodiments. In addition, examples of deformities such asspondylolisthesis are discussed; however, it is understood that thevarious prosthetic devices described herein can be adapted for usebetween not only spondylosed vertebrae, but substantially alignedvertebrae as well.

[0072] I. Lateral Correction

[0073] In many cases of deformity, such as spondylolisthesis, one ormore vertebral bodies can be displaced with respect to other vertebraeor the sacrum. In such a deformity, it is desirable to reduce the extentof displacement, by re-positioning the displaced bodies from theirprevious position. A spondylolisthesis reduction can be a technicallydemanding procedure requiring great care to prevent neurologicalimpairment and damage to surrounding soft tissue.

[0074] Referring now to FIG. 1, shown therein is a lateral view of aportion of a spinal column 10, illustrating a group of adjacent upperand lower vertebrae V1, V2, V3, V4 separated by natural intervertebraldiscs D1, D2, D3. The illustration of four vertebrae is only intended asan example. Another example would be a sacrum and one vertebrae.

[0075] As shown in the drawing, the vertebrae V2 is dislocated from thevertebrae V1 in a direction shown by arrow 22. Likewise, vertebrae V3 isdislocated in a direction shown by arrow 23 and vertebrae V4 isdislocated in a direction shown by arrow direction 24. It is desiredthat the position of vertebrae V2, V3, V4 be corrected by moving them ina direction opposite to the arrows 22, 23, 24, respectively.

[0076] Referring now to FIG. 2, for the sake of further example, two ofthe displaced vertebrae will be discussed, designated as the lowervertebrae V_(L) and the upper vertebrae V_(U). In one embodiment, someor all of the natural disc that would have been positioned between thetwo vertebrae V_(L), V_(U) is typically removed via a discectomy or asimilar surgical procedure, the details of which would be known to oneof ordinary skill in the art. Removal of the diseased or degenerateddisc results in the formation of an intervertebral space S between theupper and lower vertebrae V_(U), V_(L).

[0077] In the present embodiment, it is desired to insert a prostheticjoint into the intervertebral space S, similar to the prosthetic jointdisclosed in U.S. Ser. No. 10/042,589 filed Jan. 9, 2002, which isincorporated by reference. However, certain changes are required of theabove-referenced prosthetic joint. For the following description, theprosthetic joints discussed and described can be identical to thosedisclosed in the above-referenced patent application, with theexceptions discussed and suggested below.

[0078] Spondylolisthesis has not heretofore been corrected from thelateral surgical approach. However, in some instances, correction ofspondylolisthesis may be desirable from a lateral approach due to thepresence of vessels and/or the nervous plexus. In some embodiments, thelateral approach may be particularly pertinent when correctingspondylolisthesis in the lumbar region of the spine, although it will beunderstood that other regions of the spine are also contemplated.

[0079] Referring to FIGS. 3a and 3 b, correction of spondylolisthesiscan be addressed from a lateral approach by, for example, providing apair of bone screws 30, 32 for insertion into the vertebrae V_(U),V_(L), respectively. In one embodiment, the bone screws 30, 32 arebi-cortical. However, it is understood that the bone screws mayalternatively be uni-cortical. Moreover, the bone screws 30, 32 may beformed of a variety of materials such as any resorbable material,titanium, and PEEK. The PEEK embodiment is advantageous due to theradiotranslucent properties resulting from the use of PEEK material. Itis further understood that the bone screws 30, 32 may alternatively beof any other mechanical structure, and as such, may take the form ofpins or rivets, for example. Moreover, the bone screws 30, 32 are notlimited to having threaded portions to engage the vertebrae V_(U),V_(L).

[0080] The bone screws 30, 32 may be linked to one another via a rod 34,which is configured to rotate about both of the bone screws. It isunderstood that a variety of connecting members may be used other thanthe rod 34. For example, a non-uniform linkage member may be used tolink the bone screws 30, 32. A non-uniform linkage member may provide aplurality of slots and/or grooves that can be engaged in order to aid inits rotation about the bone screws. The rod 34 may be connected prior toinsertion of the bone screws 30, 32 into the vertebrae V_(U), V_(L), oralternatively, may be subsequently connected after placement of thescrews. By applying a rotating force to the rod 34 in the direction ofarrow 36, the upper vertebra V_(U) is encouraged back into a desiredposition relative to the lower vertebra V_(L). The rotating force can beapplied, for example, by a rotatable wrench (not shown) that can be usedby a surgeon. It is understood that the upper vertebra V_(U) may notreach entirely to a fully corrected position in relation to the lowervertebra V_(L), but the displacement can at least be reduced.

[0081] Although not depicted, in another embodiment, it is contemplatedthat the spondylosed vertebrae V_(U), V_(L) can be addressed from bothlateral directions. Thus, a pair of bone screws substantially identicalto the bone screws 30, 32 may be inserted into the vertebrae V_(U),V_(L) on the opposite side from and in the opposite direction to thebone screws 30, 32. In such an arrangement, the rod 34 can be replacedwith a ratcheting system that engages each of the bone screw pairs, andas such, the vertebrae V_(U), V_(L) can be rotated relative to oneanother to encourage the vertebrae into a desired position relative toone another.

[0082] Still further, the rod 34 may include any number and type ofengagement means to receive any number and type of rotating tools usedby a surgeon; For example, a keyed connection may provide more stabilitywhen engaging the rod 34 with a corresponding rotating tool. In otherexamples, a clamping tool may be used and corresponding clamping notchesmay be formed in the rod 34 to receive the clamping tool. Such anarrangement may aid in achieving the force necessary for rotation.

[0083] Moreover, additional rods 34 and bone screws 30, 32 arecontemplated for use in rotating the spondylosed vertebrae V_(U), V_(L)back into a desired position relative to one another. Additional rods 34and bone screws 30, 32 may provide additional stability during theprocedure.

[0084] Furthermore, although depicted as a substantially lateralinsertion, the insertion of the bone screws 30, 32 into the vertebraeV_(U), V_(L) can be slightly angled relative to the lateral direction.Such angling of the bone screws 30, 32 during insertion may provide apreferred gripping angle from which the surgeon can begin rotation ofthe vertebrae V_(U), V_(L) relative to one another.

[0085] Referring to FIGS. 4a, 5, and 6, shown therein is one embodimentof an offset intervertebral articulating prosthetic joint 40 forinsertion into the intervertebral space S (FIG. 2) to aid in thecorrection of spondylolisthesis. The articulating prosthetic joint 40extends generally along a longitudinal axis L and includes a firstarticular component 42 and a second articular component 44. Thearticular components 42, 44 cooperate to form the prosthetic joint 40which is sized and configured for disposition within the intervertebralspace S (FIG. 2) between adjacent vertebral bodies V_(U), V_(L) (FIG.2).

[0086] The prosthetic joint 40 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies to maintain or restoremotion substantially similar to the normal bio-mechanical motionprovided by a natural intervertebral disc. More specifically, thearticular components 42, 44 are permitted to pivot relative to oneanother about a number of axes, including lateral or side-to-sidepivotal movement about longitudinal axis L and anterior-posteriorpivotal movement about a transverse axis T. It should be understood thatin one embodiment of the disclosure, the articular components 42, 44 arepermitted to pivot relative to one another about any axes that lies in aplane that intersects longitudinal axis L and transverse axis T.

[0087] Furthermore, the articular components 42, 44 are permitted torotate relative to one another about a rotational axis R. Although theprosthetic joint 40 has been illustrated and described as providing aspecific combination of articulating motion, it should be understoodthat other combinations of articulating movement are also possible, suchas, for example, relative translational or linear motion, and suchmovement is contemplated as falling within the scope of the presentdisclosure.

[0088] Although the articular components 42, 44 of prosthetic joint 40may be formed from a wide variety of materials, in one embodiment of thedisclosure, the articular components 42, 44 are formed of acobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However,in alternative embodiments of the disclosure, the articular components42, 44 may be formed of other materials such as titanium or stainlesssteel, a polymeric material such as polyethylene, or any otherbiocompatible material that would be apparent to one of ordinary skillin the art.

[0089] The articular components 42, 44 each include a bearing surface46, 48, respectively, that may be positioned in direct contact withvertebral bone and is preferably coated with a bone-growth promotingsubstance, such as, for example, a hydroxyapatite coating formed ofcalcium phosphate. Additionally, the bearing surfaces 46, 48 of thearticular components 42, 44, respectively, may be roughened prior tobeing coated with the bone-growth promoting substance to further enhancebone on-growth. Such surface roughening may be accomplished by way of,for example, acid etching, knurling, application of a bead coating, orother methods of roughening that would occur to one of ordinary skill inthe art.

[0090] Articular component 42 includes a support plate 50 having anarticular surface 52 and the opposite bearing surface 46. Support plate50 is sized and shaped to substantially correspond to the size and shapeof a vertebral endplate of the adjacent vertebral body V_(L) (FIG. 2).The support plate 50 may include one or more notches 54 or other typesof indicia for receiving or engaging with a corresponding portion of asurgical instrument (not shown) to aid in the manipulation and insertionof the prosthetic joint 40 within the intervertebral space S (FIG. 2)between the adjacent vertebral bodies V_(U), V_(L) (FIG. 2). Thesurgical instrument (not shown) is preferably configured to hold thearticular components 42, 44 at a predetermined orientation and spatialrelationship relative to one another during manipulation and insertionof the prosthetic joint 40, and to release the articular components 42,44 once properly positioned between the adjacent vertebrae.

[0091] In one embodiment of the disclosure, the articular component 42includes a projection 56 having a convex shape, which may be configuredas a spherical-shaped ball (half of which is shown). It should-beunderstood that other configurations of the projection 56 are alsocontemplated, such as, for example, cylindrical, elliptical or otherarcuate configurations or possibly non-arcuate configurations. It shouldalso be understood that the remaining portion of articular component 42may take on planar or non-planar configurations, such as, for example,an angular or conical configuration extending about the projection 56.

[0092] A flange member or keel 58 extends from the bearing surface 46and is configured for disposition within a preformed opening in theadjacent vertebral endplate. As with the bearing surface 46, the keel 58may be coated with a bone-growth promoting substance, such as, forexample, a hydroxyapatite coating formed of calcium phosphate.Additionally, the keel 58 may be roughened prior to being coated withthe bone-growth promoting substance to further enhance bone on-growth.In one embodiment, the keel 58 extends along the transverse axis T andis substantially centered along the bearing surface 46. However, itshould be understood that other positions and orientations of the keel58 are also contemplated.

[0093] In one embodiment, the keel 58 transversely extends along asubstantial portion of the articular component 42. Such an embodimentwould accommodate insertion of the prosthetic joint 40 using a lateralapproach as opposed to, for example, an anterior approach. In a furtherembodiment, the keel 58 may be angled, tapered, or configured in someother shape to facilitate the functional demands of the keel. In stillanother embodiment, the keel 58 may be configured as a winged keel,including a lateral portion (not shown) extending across the main bodyportion of keel 58.

[0094] In one embodiment, the keel 58 includes three openings 60extending therethrough to facilitate bone through-growth to enhancefixation to the adjacent vertebral bodies V_(U), V_(L) (FIG. 2).However, it should be understood that any number of openings 60 may bedefined through the keel 58, including a single opening or two or moreopenings. It should also be understood that the openings 60 need notnecessarily extend entirely through the keel 58, but may alternativelyextend partially therethrough. It should further be understood that thekeel 58 need not necessarily define any openings 60 extending eitherpartially or entirely therethrough. Additionally, although the openings60 are illustrated as having a circular configuration, it should beunderstood that other sizes and configurations of openings 60 are alsocontemplated.

[0095] In one embodiment, the articular component 44 includes a supportplate 70 having an articular surface 72 and the opposite bearing surface48. Support plate 70 may be sized and shaped to substantially correspondto the size and shape of a vertebral endplate of the adjacent vertebralbody V_(U). The support plate 70 may include one or more notches 74 orother types of indicia for receiving and engaging with a correspondingportion of a surgical instrument, such as discussed above with referenceto articular component 42.

[0096] In one embodiment, the articular surface 72 includes a recess 76.In one embodiment, the recess 76 has a concave shape, and is configuredas a spherical-shaped socket. However, it should be understood thatother configurations of the recess 76 are also contemplated, such as,for example, cylindrical, elliptical or other arcuate configurations orpossibly non-arcuate configurations. The remaining portion of thearticular surface 72 can be angled or otherwise configured to facilitatethe insertion and/or use of the prosthesis.

[0097] Although the concave recess 76 is illustrated as having agenerally smooth, uninterrupted articular surface, it should beunderstood that a surface depression or cavity may be defined along aportion of the recess 76 to provide a means for clearing out matter,such as particulate debris, that is disposed between the abuttingarticular components 42, 44. In such case, the convex articular surfaceof the projection 56 may alternatively define a generally smooth,uninterrupted articular surface. In another embodiment, each of theconvex projection 56 and the concave recess 76 may define a surfacedepression to facilitate removal of particulate matter disposed betweenthe abutting articular components 42, 44.

[0098] A flange member or keel 68, configured similar to the keel 58 ofarticular component 42, extends from the bearing surface 48. In oneembodiment, the keel 68 extends along the transverse axis T and isoffset from the center of the bearing surface 48. Such an embodimentwould accommodate insertion of the prosthetic joint 40 using a lateralapproach. However, it should be understood that other shapes, positionsand orientations of the keel 68 are also contemplated. For example, inFIGS. 4b and 4 c, the keels 58 and 68 may be angled relative to thetransverse axis T to aid in the circumvention of veins, arteries, bonyportions, or other obstacles that may be in place during insertion ofthe prosthetic joint 40. Also, the keel 68 may be angled, tapered, orconfigured in some other shape to facilitate the functional demands ofthe keel. In still another embodiment, the keel 68 may be configured asa winged keel, including a transverse portion extending across the mainbody portion of the keel 68.

[0099] In one embodiment, and referring to FIG. 5, the keel 68 alsoincludes three openings 70 extending therethrough to facilitate bonethrough-growth to enhance fixation to the adjacent vertebra. However, itshould be understood that any number of openings 70 may be definedthrough keel 70, including a single opening or two or more openings. Itshould also be understood that the openings 70 need not necessarilyextend entirely through the keel 68, but may alternatively extendpartially therethrough. It should further be understood that the keel 68need not necessarily define any openings 70 extending either partiallyor entirely therethrough. Additionally, although the openings 70 areillustrated as having a circular configuration, it should be understoodthat other sizes and configurations of openings 70 are alsocontemplated. As discussed above, the bearing surfaces 46, 48 that arein direct contact with vertebral bone are preferably coated with abone-growth promoting substance. Specifically, the bearing surface 48and the surface of the keel 68 can be coated with hydroxyapatite topromote bony engagement with the adjacent vertebral body V_(U). As alsodiscussed above, the bearing surface 48 and the surface of keel 68 canbe roughened prior to application of the hydroxyapatite coating.

[0100] In some embodiments, one or both of the keels 58, 68 may includea sharp forward edge, illustrated by edge 68 a of FIG. 4. By having suchan edge, insertion of the keel into the associated vertebral body isfacilitated. Also, the edge 68 a can be of sufficient sharpness that theadjacent vertebral bodies do not require a slot for receiving the keel68, discussed in greater detail below.

[0101] Referring to FIG. 7, to accommodate insertion of the offsetprosthetic joint 40 within a spondylosed intervertebral space, thepartially corrected upper and lower vertebrae V_(U), V_(L) can beprepared to accept the prosthetic joint 40 (shown in section in FIG. 7a)therebetween. Specifically, elongate openings or slots 80, 82 may beformed along the vertebral endplates of the upper and lower vertebraeV_(L), V_(U), respectively, at a predetermined width and to apredetermined depth. The slots 80, 82 can be laterally offset from eachother to accommodate the displaced vertebrae V_(L) and/or V_(U). In oneembodiment, the elongate slots 80, 82 are rectangular-shaped and extendlaterally through the vertebrae V_(L), V_(U), respectively. In aspecific embodiment, the slots 80, 82 are formed by chiseling orcuretting. However, other methods of forming slots 80, 82 are alsocontemplated as would occur to one of ordinary skill in the art, suchas, for example, by drilling or reaming. Furthermore, for someembodiments of the prosthetic joint 40, the keels 58 and/or 68 can formtheir own corresponding slots 80, 82, respectively.

[0102] Referring to FIG. 8, in one embodiment, the upper and lowervertebrae V_(U), V_(L) may be fully corrected, and thus, an alternativearticulating prosthetic joint 90 may be used in correctingspondylolisthesis. The articulating joint 90 may be substantiallysimilar to the prosthetic joint 40 with the exception of the orientationof various elements of the articulating joint 90. For example, toaccommodate insertion into fully corrected upper and lower vertebraeV_(U), V_(L), the articulating joint 90 may include alaterally-extending keel 92 that is substantially centered on an upperarticulating component 94 of the articulating joint and alaterally-extending keel 96 that is substantially centered on a lowerarticulating component 98. Furthermore, the upper articulating component94 may include a recess 100 that is substantially centered to correspondto a substantially centered projection 102 extending from the lowerarticulating component 98. In one embodiment, the upper and lowerarticulating components 94, 98 are substantially flush with one anotherwhen disposed between fully corrected upper and lower vertebrae V_(U),V_(L).

[0103] To accommodate insertion of the offset prosthetic joint 90, thefully corrected upper and lower vertebrae V_(U), V_(L) can be preparedto accept the prosthetic joint 90 therebetween. Specifically, elongateopenings or slots 104, 106 may be formed along the vertebral endplatesof the upper and lower vertebrae V_(U), V_(L), respectively, at apredetermined width and to a predetermined depth. The slots 104, 106 canbe substantially aligned with each other to accommodate the fullycorrected upper and lower vertebrae V_(U), V_(L). In one embodiment, theelongate slots 104, 106 are rectangular-shaped and extend laterallythrough the vertebrae V_(U), V_(L), respectively. In a specificembodiment, the slots 104, 106 are formed by chiseling or curetting.However, other methods of forming slots 104, 106 are also contemplatedas would occur to one of ordinary skill in the art, such as, forexample, by drilling or reaming. Furthermore, for some embodiments ofthe prosthetic joint, the keels 92 and/or 96 can form their owncorresponding slots 104, 106, respectively.

[0104] Referring to FIG. 9, in an alternative embodiment, a slidableprosthetic joint 110 can be used to help with the lateral approach fortreating spondylolisthesis. The sliding joint 110 extends generallyalong the longitudinal axis L and includes a first slidable component112 and a second slidable component 114. The slidable components 112,114 cooperate to form the sliding joint 110 which is sized andconfigured for disposition within an intervertebral space betweenadjacent vertebral bodies.

[0105] The sliding joint 110 provides movement between the adjacentvertebral bodies to maintain or restore some of the motion similar tothe normal bio-mechanical motion provided by a natural intervertebraldisc. More specifically, the slidable components 112, 114 are permittedto translate relative to one another in the axial plane.

[0106] Although the slidable components 112, 114 of prosthetic joint 110may be formed from a wide variety of materials, in one embodiment, theslidable components 112, 114 are formed of a cobalt-chrome-molybdenummetallic alloy (ASTM F-799 or F-75). However, in alternativeembodiments, the slidable components 112, 114 may be formed of othermaterials such as titanium or stainless steel, a polymeric material suchas polyethylene, or any other biocompatible material that would beapparent to one of ordinary skill in the art. The surfaces of theslidable components 112, 114 that are positioned in direct contact withvertebral bone are preferably coated with a bone-growth promotingsubstance, such as, for example, a hydroxyapatite coating formed ofcalcium phosphate. Additionally, the surface of the slidable components112, 114 that are positioned in direct contact with vertebral bone arepreferably roughened prior to being coated with the bone-growthpromoting substance to further enhance bone on-growth. Such surfaceroughening may be accomplished by way of, for example, acid etching,knurling, application of a bead coating, or other methods of rougheningthat would occur to one of ordinary skill in the art.

[0107] Slidable component 112 includes a support plate 116 having aslidable surface 118 and an opposite bearing surface 120. Support plate116 is preferably sized and shaped to substantially correspond to thesize and shape of the vertebral endplate of an adjacent vertebra. Thesupport plate 116 can include one or more notches 122 or other types ofindicia for receiving and engaging with a corresponding portion of asurgical instrument (not shown) to aid in the manipulation and insertionof the prosthetic joint 110 within an intervertebral space betweenadjacent vertebrae. The surgical instrument (not shown) is preferablyconfigured to hold the slidable components 112, 114 at a predeterminedorientation and spatial relationship relative to one another duringmanipulation and insertion of the prosthetic joint 110, and to releasethe slidable components 112, 114 once properly positioned between theadjacent vertebrae.

[0108] A flange member or keel 124 extends from the bearing surface 120and is configured for disposition within a preformed opening in theadjacent vertebral endplate. In one embodiment, the keel 124 extendsperpendicularly from the bearing surface 120 and is approximatelycentrally located along the bearing surface 120. However, it should beunderstood that other positions and orientations of the keel 124 atealso contemplated.

[0109] In one embodiment, the keel 124 transversely extends along asubstantial portion of the support plate 114. Such an embodiment wouldaccommodate insertion of the prosthetic joint 110 using a lateralapproach. In a further embodiment, the keel 124 may be angled, tapered,or configured in some other shape to facilitate the functional demandsof the keel. In still another embodiment, the keel 124 may be configuredas a winged keel, including a transverse portion extending across themain body portion of keel 124.

[0110] The keel 124 also includes openings 126 extending therethrough tofacilitate bone through-growth to enhance fixation to the adjacentvertebra. However, it should be understood that any number of openings126 may be defined through keel 124, including a single opening or threeor more openings. It should also be understood that the openings 104need not necessarily extend entirely through the keel 124, but mayalternatively extend partially therethrough. It should further beunderstood that the keel 124 need not necessarily define any openings126 extending either partially or entirely therethrough. Additionally,although the openings 126 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 126 are also contemplated. As discussedabove, the surfaces of the slidable component 112 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 120 and thesurfaces of the keel 124 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 120 and the surfaces of keel 124 can be roughenedprior to application of the hydroxyapatite coating.

[0111] In one embodiment, the slidable component 114 includes a supportplate 128 having a slidable surface 130 and an opposite bearing surface132. Support plate 128 is preferably sized and shaped to substantiallycorrespond to the size and shape of the vertebral endplate of anadjacent vertebra. The support plate 128 can include one or more notches134 or other types of indicia for receiving and engaging with acorresponding portion of a surgical instrument, such as discussed abovewith reference to slidable element 112.

[0112] A flange member or keel 136, configured similar to the keel 124of slidable component 112, extends from the bearing surface 132. In oneembodiment, the keel 136 extends perpendicularly from the bearingsurface 132 and is offset along the bearing surface 132 to accommodatespondylosed displacements of the vertebrae. Also, the offset position ofthe keel 136 helps in the circumvention of veins, arteries, bonyportions, or other obstacles that may be in place during the insertionof the joint 110. It should be further understood that other positions,shapes, orientations, and quantities of the keel 136 are alsocontemplated. It should also be understood that the keel 136 may also bedifferently positioned, shaped or oriented, or more keels 136 can beused, for similar or additional reasons.

[0113] In one embodiment, the keel 136 transversely extends along asubstantial portion of the support plate 128. Such an embodiment wouldaccommodate insertion of the prosthetic joint 110 using a lateralapproach as opposed to another approach such as an anterior approach. Ina further embodiment, the keel 136 may be angled, tapered, or configuredin some other shape to facilitate the functional demands of the keel. Instill another embodiment, the keel 136 may be configured as a wingedkeel, including a transverse portion extending across the main bodyportion of keel 136.

[0114] The keel 136 also includes three openings 138 extendingtherethrough to facilitate bone through-growth to enhance fixation tothe adjacent vertebra. However, it should be understood that any numberof openings 138 may be defined through keel 136, including a singleopening or three or more openings. It should also be understood that theopenings 138 need not necessarily extend entirely through the keel 136,but may alternatively extend partially therethrough. It should furtherbe understood that the keel 136 need not necessarily define any openings138 extending either partially or entirely therethrough. Additionally,although the openings 138 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 138 are also contemplated. As discussedabove, the surfaces of the slidable component 114 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 132 and thesurfaces of the keel 136 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 132 and the surfaces of keel 136 can be roughenedprior to application of the hydroxyapatite coating.

[0115] In some embodiments, one or both of the keels 124, 136 mayinclude a sharp forward edge, illustrated by edges 124 a, 136 a. Byhaving such an edge, insertion of the keels 124, 136 into the associatedvertebral body is facilitated. Also, the edges 124 a, 136 a can be ofsufficient sharpness that the vertebral body does not require a slot forreceiving the keels 124, 136, respectively, discussed in greater detailbelow.

[0116] Referring to FIG. 10, to accommodate insertion of the prostheticjoint 110 within a spondylosed intervertebral space, the lower and uppervertebrae V_(L), V_(U) can be prepared to accept the prosthetic joint110 therebetween. Specifically, elongate openings or slots 142, 144, maybe formed along the vertebral endplates of the lower and upper vertebraeV_(L), V_(U), respectively, at a predetermined width and to apredetermined depth. The slots 142, 144 can be laterally offset fromeach other to accommodate the displaced vertebrae V_(L) and/or V_(U). Inone embodiment of the disclosure, the elongate slots 142, 144 arerectangular-shaped and extend laterally through the vertebrae V_(L),V_(U). In a specific embodiment, the slots 142, 144 are formed bychiseling or curetting. However, other methods of forming slots 142, 144are also contemplated as would occur to one of ordinary skill in theart, such as, for example, by drilling or reaming. Furthermore, for someembodiments of the prosthetic joint, the keels 124 and/or 136 can formtheir own corresponding slots.

[0117] Referring to FIG. 11, in one embodiment, the upper and lowervertebrae V_(U), V_(L) may be fully corrected, and thus, an alternativearticulating joint 150 may be used in correcting spondylolisthesis. Thearticulating joint 150 may be substantially similar to the articulatingjoint 110 with the exception of the orientation of the keel. Forexample, to accommodate insertion into fully corrected upper and lowervertebrae V_(U), V_(L), the articulating joint 150 may include a keel152 that is substantially centered on an upper articulating component154 of the articulating joint and a keel 156 that is substantiallycentered on a lower articulating component 158. In one embodiment, theupper and lower articulating components 154, 158 are substantially flushwith one another when disposed between fully corrected upper and lowervertebrae V_(U), V_(L).

[0118] To accommodate insertion of the offset prosthetic joint 150, thefully corrected upper and lower vertebrae V_(U), V_(L) can be preparedto accept the prosthetic joint 150 therebetween. Specifically, elongateopenings or slots 160, 162 are formed along the vertebral endplates ofthe upper and lower vertebrae V_(U), V_(L), at a predetermined width andto a predetermined depth. The slots 160, 162 can be substantiallyaligned with each other to accommodate the fully corrected upper andlower vertebrae V_(U), V_(L). In one embodiment, the elongate slots 160,162 are rectangular-shaped and extend laterally through the vertebraeV_(U), V_(L), respectively. In a specific embodiment, the slots 160, 162are formed by chiseling or curetting. However, other methods of formingslots 160, 162 are also contemplated as would occur to one of ordinaryskill in the art, such as, for example, by drilling or reaming.Furthermore, for some embodiments of the prosthetic joint, the keels 152and/or 156 can form their own corresponding slots 160, 162,respectively.

[0119] Referring to FIGS. 12 and 13, fusion plates and cages can also beoutfitted with one or more keels and laterally inserted, in a mannerconsistent with the motion-preserving embodiments discussed above andsuperior to conventional fusion arrangements. Referring specifically toFIG. 12, a lateral prosthesis 170 includes a cage 172, an upper keel174, and a lower keel 176. The cage 172 connects to the upper and lowerkeels 174, 176 through support plates 178, 180, respectively. The cage172 can include many features of the LT-CAGE™ lumbar tapered fusiondevice provided by Medtronic Sofamor Danek of Memphis, Tenn., and can beused to contain biological material and/or other bone growth promotingmaterials. Also, the lateral keels 174, 176 can help to maintain thecorrected vertebrae displacement while fusion is occurring.

[0120] Referring to FIG. 13, a prosthesis 190 includes a plate 192, anupper keel 194, a lower keel 196, an upper support plate 198, and alower support plate 200. The plate 192 can be used to maintain a desireddistance between the two support plates 198, 200 and promote fusion.Since the plate 192 can be relatively thin, the remainder of the discspace can be filled with biological material, bone material, and orother bone growth promoting materials.

[0121] II. Anterior Correction

[0122] In some instances, correction of spondylolisthesis may bedesirable from the anterior approach. Referring to FIGS. 14-16, showntherein is an intervertebral articulating prosthetic joint 210 accordingto an alternative embodiment of the present disclosure. The prostheticjoint 210 extends generally along a longitudinal axis L and includes afirst articular component 212 and a second articular component 214. Thearticular components 212, 214 cooperate to form the articulating joint210 which is sized and configured for disposition within anintervertebral space between a pair of vertebral bodies, such as theintervertebral space S between the adjacent vertebral bodies V_(U),V_(L).

[0123] The prosthetic joint 210 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies V_(U), V_(L) to maintainor restore motion substantially similar to the normal bio-mechanicalmotion provided by a natural intervertebral disc. More specifically, thearticular components 212, 214 are permitted to pivot relative to oneanother about a number of axes, including lateral or side-to-sidepivotal movement about longitudinal axis L and anterior-posteriorpivotal movement about a transverse axis T. It should be understood thatin one embodiment, the articular components 212, 214 are permitted topivot relative to one another about any axes that lies in a plane thatintersects longitudinal axis L and transverse axis T. Additionally, thearticular components 212, 214 are permitted to rotate relative to oneanother about a rotational axis R. Although the prosthetic joint 210 hasbeen illustrated and described as providing a specific combination ofarticulating motion, it should be understood that other combinations ofarticulating movement are also possible, such as, for example, relativetranslational or linear motion, and are contemplated as falling withinthe scope of the present disclosure.

[0124] Although the articular components 212, 214 of prosthetic joint210 may be formed from a wide variety of materials, in one embodiment,the articular components 212, 214 are formed of acobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However,in alternative embodiments, the articular components 212, 214 may beformed of other materials such as titanium or stainless steel, apolymeric material such as polyethylene, or any other biocompatiblematerial that would be apparent to one of ordinary skill in the art. Thesurfaces of the articular components 212, 214 that are positioned indirect contact with vertebral bone may be coated with a bone-growthpromoting substance, such as, for example, a hydroxyapatite coatingformed of calcium phosphate. Additionally, the surface of the articularcomponents 212, 214 that are positioned in direct contact with vertebralbone may be roughened prior to being coated with the bone-growthpromoting substance to further enhance bone on-growth. Such surfaceroughening may be accomplished by way of, for example, acid etching,knurling, application of a bead coating, or other methods of rougheningthat would occur to one of ordinary skill in the art.

[0125] Articular component 212 includes a support plate 216 having anarticular surface 218 and an opposite bearing surface 220. Support plate216 may be sized and shaped to substantially correspond to the size andshape of the vertebral endplate of an adjacent vertebra. The supportplate 216 can include one or more notches 222 or other types of indiciafor receiving and engaging with a corresponding portion of a surgicalinstrument (not shown) to aid in the manipulation and insertion of thearticulating joint 210 within an intervertebral space between adjacentvertebrae. The surgical instrument (not shown) is preferably configuredto hold the articular components 212, 214 at a predetermined orientationand spatial relationship relative to one another during manipulation andinsertion of the articulating joint 210, and to release the articularcomponents 212, 214 once properly positioned between the adjacentvertebrae.

[0126] In one embodiment, the articular surface 218 includes aprojection 224 having a convex shape, which may be configured as aspherical-shaped ball (half of which is shown). It should be understoodthat other configurations of the projection 224 are also contemplated,such as, for example, cylindrical, elliptical or other arcuateconfigurations or possibly non-arcuate configurations. It should also beunderstood that the remaining portion of articular surface 218 may takeon planar or non-planar configurations, such as, for example, an angularor conical configuration extending about the projection 224.

[0127] In one embodiment, the convex articular surface of the projection224 is interrupted by a surface depression or cavity 226 extending alongthe projection 224. In one embodiment, the surface depression 226 isconfigured as a groove. However, it should be understood that othertypes of surface depressions are also contemplated, including nodepression at all. One purpose of the groove 226 is to facilitate theremoval of matter disposed between abutting portions of the articularcomponents 212, 214. More specifically, the groove 226 may aid inclearing out matter such as, for example, particulate material, that isdisposed between the abutting articular surfaces of components 212, 214.

[0128] A flange member or keel 230 extends from the bearing surface 220and is configured for disposition within a preformed opening in theadjacent vertebral endplate. In one embodiment, the keel 230 extendsperpendicularly from the bearing surface 220 and is approximatelycentrally located along the bearing surface 220. However, it should beunderstood that other positions and orientations of the keel 230 arealso contemplated.

[0129] In one embodiment, the keel 230 extends along substantially theentire length of the support plate 216. Such an embodiment wouldaccommodate insertion of the articulating joint 210 using an anteriorapproach. In a further embodiment, the keel 230 may be angled, tapered,or configured in some other shape to facilitate the functional demandsof the keel. In still another embodiment, the keel 230 may be configuredas a winged keel, including a transverse portion (not shown) extendingacross the main body portion of keel 230.

[0130] The keel 230 also includes a pair of openings 232 extendingtherethrough to facilitate bone through-growth to enhance fixation tothe adjacent vertebra. However, it should be understood that any numberof openings 232 may be defined through keel 230, including a singleopening or three or more openings. It should also be understood that theopenings 232 need not necessarily extend entirely through the keel 230,but may alternatively extend partially therethrough. It should furtherbe understood that the keel 230 need not necessarily define any openings232 extending either partially or entirely therethrough. Additionally,although the openings 232 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of the openings 232 are also contemplated. As discussedabove, the surfaces of the articular component 212 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 220 and thesurfaces of the keel 230 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 220 and the surfaces of keel 230 can be roughenedprior to application of the hydroxyapatite coating.

[0131] In one embodiment, the articular component 214 includes a supportplate 240 having an articular surface 242 and an opposite bearingsurface 244. Support plate 240 may be sized and shaped to substantiallycorrespond to the size and shape of the vertebral endplate of anadjacent vertebra. The support plate 240 can include one or more notches246 or other types of indicia for receiving and engaging with acorresponding portion of a surgical instrument, such as discussed abovewith reference to articular component 212.

[0132] In one embodiment, the articular surface 242 includes a recess250, which has a convex shape, such as that of a spherical-shapedsocket. However, it should be understood that other configurations ofthe recess 250 are also contemplated, such as, for example, cylindrical,elliptical or other arcuate configurations or possibly non-arcuateconfigurations. The remaining portion of the articular surface 242 canbe angled or otherwise configured to facilitate the insertion and/or useof the articulating joint 210.

[0133] Although the concave recess 250 is illustrated as having agenerally smooth, uninterrupted articular surface, it should beunderstood that a surface depression or cavity may be defined along aportion of the recess 250 to aid in clearing out matter, such asparticulate debris, that is disposed between the abutting articularsurfaces of articular components 212, 214. In such case, the convexarticular surface of the ball 224 may alternatively define a generallysmooth, uninterrupted articular surface. In another embodiment, each ofthe convex projection 224 and the concave recess 250 may define asurface depression to facilitate removal of particulate matter disposedbetween the abutting articular surfaces.

[0134] A flange member or keel 260, configured similar to the keel 230of articular component 212, extends from the bearing surface 244. In oneembodiment, the keel 260 extends perpendicularly from the bearingsurface 244 and is approximately centrally located along bearing surface244. However, it should be understood that other positions andorientations of the keel 260 are also contemplated. It should also beunderstood that the articular component 214 may include two or morekeels 260 extending from the bearing surface 244.

[0135] In one embodiment, the keel 260 extends along substantially theentire length of the support plate 240. Such an embodiment wouldaccommodate insertion of the prosthetic joint 210 using an anteriorapproach. In a further embodiment, the keel 260 may be angled, tapered,or configured in some other shape to facilitate the functional demandsof the keel. In still another embodiment, the keel 260 may be configuredas a winged keel, including a transverse portion (not shown) extendingacross the main body portion of keel 260.

[0136] The keel 260 also includes a pair of openings 262 extendingtherethrough to facilitate bone through-growth to enhance fixation tothe adjacent vertebra. However, it should be understood that any numberof openings 262 may be defined through keel 260, including a singleopening or three or more openings. It should also be understood that theopenings 262 need not necessarily extend entirely through the keel 260,but may alternatively extend partially therethrough. It should furtherbe understood that the keel 260 need not necessarily define any openings262 extending either partially or entirely therethrough. Additionally,although the openings 262 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 262 are also contemplated. As discussedabove, the surfaces of the articular component 214 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 244 and thesurfaces of the keel 260 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 244 and the surfaces of keel 260 can be roughenedprior to application of the hydroxyapatite coating.

[0137] In some embodiments, one or both of the keels 230, 260 mayinclude a sharp forward edge, illustrated by edge 260 a of FIG. 14. Byhaving such an edge, insertion of the keel into the associated vertebralbody is facilitated. Also, the edge 260 a can be of sufficient sharpnessthat the vertebral body does not require a slot for receiving the keel260, discussed in greater detail below.

[0138] To work with dislocated vertebrae, such as vertebrae V1-V5 ofFIG. 1 associated with spondylolisthesis, it is recognized that the taskof fully correcting and aligning a spondylosed segment may not beachievable or desirable by the surgeon. Therefore, the basicarticulation described in co-pending and presently incorporated U.S.Ser. No. 10/042,589 now has an associated displacement to correspond tothe vertebrae displacement. That is, for the amount of displacementbetween two adjacent spondylosed vertebrae, the articulation of theprosthetic joint 210 is made to correspond thereto. In some embodiments,such displacement can be effected by positioning one or more of theprojection 224 in an offset position on the articular surface 218 of thearticular component 212, and positioning one or more of the recess 250in an offset position on the articular surface 242 of the articularcomponent 214. This allows an uncorrected or partially correcteddisplacement to be mobilized.

[0139] More particularly, and referring to FIGS. 14 and 17, theprojection 224 is offset relative to the articular surface 218. Forexample, when the lower vertebra (V_(L) of FIG. 17) is offset in theposterior direction (illustrated by arrow P in FIG. 17), the articularcomponent 212 may be configured such that the projection 224 is offsetin the anterior direction relative to the articular surface 218.Continuing this example, the upper vertebra V_(U) is therefore offsetfrom the lower vertebra V_(L) in the anterior direction (illustrated byarrow A in FIG. 17), and thus, the articular component 214 may beconfigured such that the recess 250 is offset in the posterior directionrelative to the articular surface 242. In this manner, the articularcomponents 212, 214 can be configured to engage one another via theprojection 224 and the recess 250, yet be offset from one another toaccommodate the spondylosed relationship of the upper and lowervertebrae V_(U), V_(L) of FIG. 17.

[0140] Referring now to FIG. 16, in another embodiment, the articulatingjoint 210 may be modified such that the support plate 216 includes anextended section 270 to accommodate a more pronounced displacementrelative to FIG. 17 (illustrated by arrow 272) and/or provide additionalstability against subluxation. The projection 224 may be positioned onthe extended section 270 to provide for the more pronounced displacementbetween articular components 212, 214.

[0141] Referring to FIGS. 2 and 17, to accommodate insertion of theprosthetic joint 210 within the intervertebral space S, the upper andlower vertebrae V_(U), V_(L) can be prepared to accept the prostheticjoint 210 therebetween. Specifically, elongate openings or slots 280,282 are formed along the vertebral endplates of the upper and lowervertebrae V_(U), V_(L), respectively, at a predetermined width and to apredetermined depth. In one embodiment, the elongate slots 280, 282 arerectangular-shaped and extend from an anterior side 284 of the vertebraeV_(U), V_(L) toward a posterior side. In a specific embodiment, theslots 280, 282 are formed by chiseling or curetting. However, othermethods of forming the slots 280, 282 are also contemplated as wouldoccur to one of ordinary skill in the art, such as, for example, bydrilling or reaming. Furthermore, for some embodiments of the prostheticjoint 210, the keels 230 and/or 260 can form their own correspondingslots 280, 282, respectively. The preparation and example sizes of theslots 280, 282 are described in further detail in co-pending andpresently incorporated U.S. Ser. No. 10/042,589.

[0142] Referring now to FIGS. 18-20, in other embodiments, one or bothof the articular components 212, 214 may include different numbers ofkeels and/or modified keels. Referring specifically to FIG. 18, twokeels, designated 290 and 292, extend from the bearing surface 244 andare configured for disposition within preformed openings in the adjacentvertebral endplate. In one embodiment, both keels 290, 292 extendperpendicularly from the bearing surface 244 and are parallel andequally spaced along a central portion of the bearing surface 244.

[0143] Referring specifically to FIG. 19, two keels, designated 294 and296, extend from the bearing surface 224 and are configured fordisposition within preformed openings in the adjacent vertebralendplate. In one embodiment, both keels 294, 296 extend perpendicularlyfrom the bearing surface 224 and are parallel and equally spaced along acentral portion of the bearing surface 224. It should be understood thatother positions and orientations of the keels 290, 292, 294, and 296 arealso contemplated.

[0144] Referring specifically to FIG. 20, a keel 298 extends from thebearing surface 244 similar to the keel 260 of FIG. 14, except that thekeel 298 includes a laterally-extending or “winged” portion 300 opposingthe bearing surface 244. The winged portion 300 can provide severalfunctions, including maintaining the bearing surface 244 tightly againstthe body V_(U), and substantially preventing any longitudinal movementof the articular component 214. Similarly, a keel 302 extends from thebearing surface 224 and includes a winged portion 304 opposing thebearing surface 224. The winged portion 304 can provide severalfunctions, including maintaining the bearing surface 224 tightly againstthe body V_(L), and substantially preventing any longitudinal movementof the articular component 212.

[0145] Referring to FIGS. 21-23, to accommodate insertion of theabove-described alternative prosthetic joints 210 within theintervertebral space S, the upper and lower vertebrae V_(U), V_(L) canbe prepared to accept each of the articulating joints 210 therebetween.Referring specifically to FIG. 21, for the configuration of theprosthetic joint 210 of FIG. 18, multiple slots 310 and 312 are formedalong the vertebral endplate of the upper vertebrae V_(U), and a singleslot 314 is formed along the vertebral endplate of the lower vertebraeV_(L). Referring specifically to FIG. 22, for the configuration of theprosthetic joint 210 of FIG. 19, multiple slots 316, 318 and 320, 322are formed along the vertebral endplates of the upper vertebrae V_(U),and lower vertebrae V_(L), respectively. Referring specifically to FIG.23, for the configuration of the prosthetic joint 210 of FIG. 20, wingedslots 324, 326 are formed along the vertebral endplates of the uppervertebrae V_(U) and the lower vertebrae V_(L), respectively. Thepreparation of the slots 310, 312, 314, 316, 318, 320, 322, 324, 326 canbe accomplished in a similar manner to those discussed above withrespect to FIG. 17. For the winged slots 324, 326, a standard chisel canbe used, or alternatively, a unique wing-shaped chisel can be used.

[0146] Referring to FIG. 24, in addition to the prosthetic joint 210, awoven orthopedic implant 330 can be used to act as an artificialligament between the two vertebrae V_(U), V_(L). One embodiment of thewoven implant 330 is disclosed in U.S. Ser. No. 10/082,579, which isincorporated by reference. The implant 330 functions as a naturalligament would function, and helps to stabilize and further secure thetwo vertebrae V_(U), V_(L) together, and helps to discourage furtherdisplacement (or prevent the displacement from returning to the way itwas pre-surgery).

[0147] Referring to FIGS. 25 and 26, it is contemplated that a parsfracture, such as is illustrated by a fracture in a bony element 332that connects a posterior element, such as an articular process 334 tothe vertebra V_(L), may also be treated during correction ofspondylolisthesis from the anterior approach. It is understood that thefractured bony element 332 is exaggerated in the FIG. 25 for the sake ofimproved clarity. The pars fracture can be repaired by driving a lagscrew 336 having a threaded portion 336 a and a non-threaded portion 336b into an opening 338 in the vertebral body V_(L), through the bonyelement 332, and into the articular process 334. In some embodiments,all or part of the opening 338 can be pre-drilled with a drill or chisel(not shown). The lag screw 336 is inserted and accessed through theanterior direction, and multiple screws can be used to repair multipleprocesses. By capturing the fractured posterior element and tighteningthe lag screw 336, the vertebrae V_(L) is repaired.

[0148] III. Transforaminal Prosthetic Joint

[0149] In some instances, it is often difficult to approach and clear 4defective intervertebral disc space due to potential damage to importantanatomical structures such as nerve roots, dura, ligamentum flavum andinterspinous ligament. For example, preservation of the ligamentousstructures is of great importance to restore biomechanical stability ofthe, segment and its adjacent counterparts. In these situations, atransforaminal approach may allow clearance of the entire intervertebraldisc space by opening the neuroforamen on one side. After appropriateclearance, it is possible to achieve further enlargement of the clearedintervertebral compartment by posterior trans-pedicle distraction. Whilethis approach has been used for fusion techniques, such asTransforaminal Lumbar Interbody Fusion, or TLIF, it has not heretoforebeen used with motion preserving implants.

[0150] Referring to FIG. 27, in a transforaminal approach, the disc V isapproached as shown by the arrow 400. The approach is between aposterior approach and a lateral approach, and in some cases, only oneside of the disc needs to be exposed (right or left) in order to performthe procedure.

[0151] Referring to FIGS. 28-30, shown therein is an intervertebralarticulating prosthetic joint 410 according to another form of thepresent disclosure. The articulating joint 410 extends generally along alongitudinal axis L and includes a first articular component 412 and asecond articular component 414. The articular components 412, 414cooperate to form the articulating joint 410 which is sized andconfigured for disposition within an intervertebral space betweenadjacent vertebral bodies.

[0152] The prosthetic joint 410 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies to maintain or restoremotion substantially similar to the normal bio-mechanical motionprovided by a natural intervertebral disc. More specifically, thearticular components 412, 414 are permitted to pivot relative to oneanother about a number of axes, including lateral or side-to-sidepivotal movement about longitudinal axis L and anterior-posteriorpivotal movement about a transverse axis T. It should be understood thatin one embodiment, the articular components 412, 414 are permitted topivot relative to one another about any axes that lies in a plane thatintersects longitudinal axis L and transverse axis T. Additionally, thearticular components 412, 414 are preferably permitted to rotaterelative to one another about a rotational axis R. Although thearticulating joint 410 has been illustrated and described as providing aspecific combination of articulating motion, it should be understoodthat other combinations of articulating movement are also possible andare contemplated as falling within the scope of the present disclosure.It should also be understood that other types of articulating movementare also contemplated, such as, for example, relative translational orlinear motion.

[0153] Although the articular components 412, 414 of prosthetic joint410 may be formed from a wide variety of materials, in one embodiment,the articular components 412, 414 are formed of acobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However,in alternative embodiments, the articular components 412, 414 may beformed of other materials such as titanium or stainless steel, apolymeric material such as polyethylene, or any other biocompatiblematerial that would be apparent to one of ordinary skill in the art.

[0154] The surfaces of the articular components 412, 414 that arepositioned in direct contact with vertebral bone are preferably coatedwith a bone-growth promoting substance, such as, for example, ahydroxyapatite coating formed of calcium phosphate. Additionally, thesurface of the articular components 412, 414 that are positioned indirect contact with vertebral bone are preferably roughened prior tobeing coated with the bone-growth promoting substance to further enhancebone on-growth. Such surface roughening may be accomplished by way of,for example, acid etching, knurling, application of a bead coating, orother methods of roughening that would occur to one of ordinary skill inthe art.

[0155] Articular component 412 includes a support plate 416 having anarticular surface 418 and an opposite bearing surface 420. Support plate416 may be sized and shaped to substantially correspond to the size andshape of the vertebral endplate of an adjacent vertebra. In oneembodiment, the support plate 416 is shaped to facilitate atransforaminal insertion approach. As such, the support plate 416includes curved side portions 422 a, 422 b, which are defined as thegenerally elongated portions of the support plate 416 extending betweenarticular surface 418 and the bearing surface 420. Although not shown,the support plate 416 can include one or more notches or other types ofindicia for receiving and engaging with a corresponding portion of asurgical instrument (also not shown) to aid in the manipulation andinsertion of the prosthetic joint 410 within an intervertebral spacebetween adjacent vertebrae. The surgical instrument (not shown) ispreferably configured to hold the articular components 412, 414 at apredetermined orientation and spatial relationship relative to oneanother during manipulation and insertion of the prosthetic joint 410,and to release the articular components 412, 414 once properlypositioned between the adjacent vertebrae.

[0156] In one embodiment, the articular surface 418 includes aprojection 424 having a convex shape, which may be configured as aspherical-shaped ball (half of which is shown). It should be understoodthat other configurations of the projection 424 are also contemplated,such as, for example, cylindrical, elliptical or other arcuateconfigurations or possibly non-arcuate configurations. It should also beunderstood that the remaining portion of articular surface 418 may takeon planar or non-planar configurations, such as, for example, an angularor conical configuration extending about the projection 424.

[0157] A flange member or keel 426 extends from the bearing surface 410and is configured for disposition within a preformed opening in theadjacent vertebral endplate. In one embodiment, the keel 426 extendsperpendicularly from the bearing surface 420 and is approximatelycentrally located along the bearing surface 420. However, it should beunderstood that other positions and orientations of the keel 426 arealso contemplated.

[0158] In one embodiment, the keel 426 transversely extends along asubstantial portion of the support plate 416. The keel 426 is curved,generally in a direction similar to the arrow 400 of FIG. 27. The degreeof curvature of the keel 426 may be substantially similar to andcongruous with the degree of curvature of the side portions 422 a, 422b. Such an embodiment would accommodate insertion of the prostheticjoint 410 using a transforaminal approach as opposed to the anterior orlateral approaches discussed above. In a further embodiment, the keel426 may be angled, tapered, or configured in some other shape tofacilitate the functional demands of the keel. In still anotherembodiment, the keel 426 may be configured as a winged keel, including atransverse portion (not shown) extending across the main body portion ofkeel 426.

[0159] The keel 426 also includes three openings 428 extendingtherethrough to facilitate bone through-growth to enhance fixation tothe adjacent vertebra. However, it should be understood that any numberof openings 428 may be defined through keel 426, including a singleopening or three or more openings. It should also be understood that theopenings 428 need not necessarily extend entirely through the keel 426,but may alternatively extend partially therethrough. It should furtherbe understood that the keel 426 need not necessarily define any openings428 extending either partially or entirely therethrough. Additionally,although the openings 428 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 428 are also contemplated. As discussedabove, the surfaces of the articular component 412 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 420 and thesurfaces of the keel 426 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 420 and the surfaces of keel 426 can be roughenedprior to application of the hydroxyapatite coating.

[0160] In one embodiment, the articular component 414 includes a supportplate 430 having an articular surface 432 and an opposite bearingsurface 434. Support plate 430 may be sized and shaped to substantiallycorrespond to the size and shape of the vertebral endplate of anadjacent vertebra. In one embodiment, the support plate 430 is shaped tofacilitate a transforaminal insertion approach. As such, the supportplate 416 includes curved side portions 436 a, 436 b, which are definedas the generally elongated portions of the support plate 430 extendingbetween articular surface 432 and the bearing surface 434. Although notshown, the support plate 430 can include one or more notches or othertypes of indicia for receiving and engaging with a corresponding portionof a surgical instrument, such as discussed above with reference toarticular element 412.

[0161] In one embodiment, the articular surface 432 includes a recess440 having a concave shape, which may be configured as aspherical-shaped socket. However, it should be understood that otherconfigurations of the recess 440 are also contemplated, such as, forexample, cylindrical, elliptical or other arcuate configurations orpossibly non-arcuate configurations. The remaining portion of thearticular surface 432 can be angled or otherwise configured tofacilitate the insertion and/or use of the prosthesis.

[0162] Although the concave recess 440 is illustrated as having agenerally smooth, uninterrupted articular surface, it should beunderstood that a surface depression or cavity may be defined along aportion of the recess 440 to provide a means for clearing out matter,such as particulate debris, that is disposed between the abuttingarticular surfaces of components 412, 414. In such case, the convexarticular surface of the ball 424 may alternatively define a generallysmooth, uninterrupted articular surface. In another embodiment, each ofthe convex projection 424 and the concave recess 440 may define asurface depression to facilitate removal of particulate matter disposedbetween the abutting articular surfaces.

[0163] A flange member or keel 450, configured similar to the keel 426of articular component 412, extends from the bearing surface 434. In oneembodiment, the keel 450 can be centrally located, and is positioneddirectly or parallel in-line with the keel 450. The keel 450 is curved,in a direction similar to the keel 426 and the arrow 400 of FIG. 27. Thedegree of curvature of the keel 450 may be substantially similar to andcongruous with the degree of curvature of the side portions 436 a, 436b. Such an embodiment would accommodate insertion of the prostheticjoint 410 using a transforaminal approach as opposed to the anterior orlateral approaches discussed above. In some embodiments, the position ofthe keel 450 can be offset to help circumvent veins, arteries, bonyportions, or other obstacles that may be in place during the insertionof the joint 410.

[0164] It should also be understood that the keel 450 may also bedifferently positioned, shaped or oriented, or more keels 450 can beused, for similar or additional reasons. Also, the keel 450 may beangled, tapered, or configured in some other shape to facilitate thefunctional demands of the keel. In still another embodiment, the keel450 may be configured as a winged keel, including a transverse portion(not shown) extending across the main body portion of keel 450.

[0165] In one embodiment, the keel 450 also includes three openings 452extending therethrough to facilitate bone through-growth to enhancefixation to the adjacent vertebra. However, it should be understood thatany number of openings 452 may be defined through keel 450, including asingle opening or three or more openings. It should also be understoodthat the openings 452 need not necessarily extend entirely through thekeel 450, but may alternatively extend partially therethrough. It shouldfurther be understood that the keel 450 need not necessarily define anyopenings 452 extending either partially or entirely therethrough.Additionally, although the openings 452 are illustrated as having acircular configuration, it should be understood that other sizes andconfigurations of openings 452 are also contemplated. As discussedabove, the surfaces of the articular component 414 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 434 and thesurfaces of the keel 450 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 434 and the surfaces of keel 450 can be roughenedprior to application of the hydroxyapatite coating.

[0166] In some embodiments, one or both of the keels 426, 450 mayinclude a sharp forward edge, illustrated by edges 460, 462,respectively, of FIG. 28c. By having such an edge, insertion of the keelinto the associated vertebral body is facilitated. Also, the edges 460,462 can be of sufficient sharpness that the vertebral bodies do notrequire a slot for receiving the keels 426, 450, discussed in greaterdetail below.

[0167] Referring to FIGS. 31a and 31 b, to accommodate insertion of theprosthetic joint 410 within the intervertebral space, the upper andlower vertebrae V_(U), V_(L) can be prepared to accept the prostheticjoint 410 therebetween. Referring specifically to FIG. 31a, for theconfiguration of the prosthetic joint 410 of FIGS. 28-30, multiple slots470, 472 are formed along the vertebral endplates of the upper vertebraeV_(U) and the lower vertebrae V_(L). The slots 470, 472 can be createdby the keels 426, 450 themselves, or can be prepared beforehand.

[0168] Referring also to FIG. 32, it may be desirable to prepare one ormore of the slots 470, 472 before the prosthetic joint 410 is insertedbetween the upper and lower vertebrae V_(U), V_(L). The slots 470, 472can be curved, as illustrated by the slot 472, in accordance with thecurved keels 426, 450, to facilitate the movement of the prostheticjoint 410 during insertion.

[0169] Referring to FIGS. 33-35, as an alternative to chiseling, whichprovides only for the cutting of straight slots, a milling guide 500 maybe used in conjunction with a milling tool 502 to cut the curved slots470, 472 (represented by 472 in FIG. 32) in the upper and lowervertebral bone V_(U), V_(L). The milling guide 500 and milling tool 502may be formed of any material including biocompatible materials such astitanium. The milling guide 500 includes an elongated curved member 503,which defines a curved opening 504 to correspond to the shape of thedesired curve for the slots 470, 472. Of course, the degree of curvatureof the milling guide 500, and therefore the curved opening 504, may varydepending on the desired curve of the slots 470, 472. In one embodiment,the milling guide 500 is formed of a pliable material that retains arigid shape upon reforming such that the degree of curvature of thecurved opening 504 may be altered without having to swap out millingguides. The milling guide 500, and therefore the curved opening 504, isalso of sufficient length so that if the slots 470, 472 need to becontinued through any posterior elements of the vertebrae, suchextension of the slots can be accomplished at the same time.

[0170] Referring specifically to FIGS. 34a and 34 b, in one embodiment,the milling tool 502 includes a milling bit 510 that is positioned to berotated and translated in the curved opening 504. In one embodiment, themilling bit 510 is a double fluted routing bit, that may extendsimultaneously into the upper and lower vertebrae V_(U), V_(L).

[0171] The milling bit 510 is also adapted to receive a translationalforce such that the milling bit can be moved back and forth in thecurved opening 504. Referring to FIG. 34b, in one embodiment, a millingbit handle 530 is connected in any conventional manner to a housing 522(a portion of which is shown). The handle 530 extends from the housing522 and through a slot 532 formed in a proximal end 534 of the millingguide 500 relative to a surgeon (not depicted). As such, the handle 530can be translated by a surgeon, thereby translating the milling bit 510through the curved opening 504. In this manner, the handle 530 isadapted to impart translational movement to the milling bit 510. Toaccommodate movement of the milling bit 510 within the curved opening504, a pair of bearing assemblies 512, 514 may be positioned adjacent tothe housing 522 to guide the milling bit 510 along the curved opening.

[0172] The housing 522 houses a rotation assembly, which, in oneembodiment, is a gear assembly 524. The gear assembly 524 includes adrive gear 526 connected to and extending annularly around a rotatableshaft 528. The shaft 528 is rotatable via an external source representedby power supply 516 (FIG. 35). In one embodiment, the shaft 528 ishoused within the handle 530.

[0173] The gear assembly 524 further includes a bit gear 531, which isconnected to and extends annularly around the milling bit 510. The bitgear 531 is positioned on the milling bit 510 such that the bit gear isorthogonal relative to and in contact with the drive gear 526. Thus,rotation of the shaft 528 imparts rotation to the milling bit 510 viathe gear assembly 524. A pair of annular shoulders 535, 536 are alsoconnected to the milling bit 510 such that the milling bit can easilymove back and forth through the curved opening 504 without slippage inthe upper or lower directions as viewed in FIG. 34b. It is understoodthat the gear assembly 524 is merely exemplary of an assembly that maybe used to impart rotational motion to the milling bit 510. Other typesof rotation-imparting assemblies are contemplated as falling within thepresent disclosure such as pneumatic-type systems.

[0174] Referring to FIG. 34c, in one such embodiment, a pneumatic system538 may be employed to impart rotation to the milling bit 510. In oneembodiment, a Medtronic Midas Rex® Legend™ motor is used to supply power(represented by P) to the pneumatic system. A conventional valve 539 isused to control the air flow and pressure supplied to rotate the millingbit 510. In still other embodiments, manual or combination powersupplies are contemplated as being the preferred power supply 516 (FIG.34b) and P (FIG. 34c).

[0175] Referring again to FIGS. 34a and 34 b, a guide handle 540 isfurther provided such that the milling guide 500 is independentlymovable relative to the milling bit 510. Thus in one embodiment, themilling guide 500 can be held via the guide handle 540 with one handwhile the milling bit 510 may be moved within the curved opening 504 viathe handle 530 with the other hand. In some embodiments, the handle 530may extend through the guide handle 540 as shown in FIG. 34b. As aresult, and referring to FIG. 35, the milling bit 510 is adapted torotate in a direction indicated by arrow R1, and is adapted to betranslated through the curved opening 504 in the directions indicated byarrow R2.

[0176] In operation, the milling guide 500 and the milling tool 502 canbe used to cut a slot, such as the slot 472, to prepare the vertebralbody V_(L) to receive the lower portion of the prosthetic joint 410. Thesurgeon first selects the desired amount of curvature to impart to theslot 472 and selects or configures the corresponding milling guide 500.The surgeon then approaches the vertebral body V_(L) from thetransforaminal approach to position the milling guide 500 into the discspace between the upper and lower vertebrae V_(U), V_(L) and to abut themilling bit 510 against the upper and lower vertebrae V_(U), V_(L). Uponproper positioning, the surgeon may then actuate the milling tool 502via the power supply 516 to begin cutting into the upper and lowervertebrae V_(U), V_(L) with the milling bit 510.

[0177] The milling guide 500 may be held by the surgeon or via anexternal instrument such that the milling guide is stationary duringtranslational movement of the milling bit 510 through the milling guide.The curvature of the milling guide 500 guides the milling bit 510transforaminally through the upper and lower vertebrae V_(U), V_(L) tocut a transforaminal slot, such as the slot 472 depicted in the lowervertebra V_(L) FIG. 32, to prepare the upper and lower vertebrae toreceive the transforaminal prosthetic joint 410.

[0178] In an alternative embodiment, the keels of the prosthetic joint410 may take alternative shapes and configurations to assist in thecurved, transforaminal approach used in inserting the joint. Referringto FIGS. 36-38, the keels, designated 550 and 560, extend from thebearing surfaces 434 and 420, respectively. The keels 550, 560 arerelatively short and thus extend along a short portion of the bearingsurfaces 434, 420, respectively, in comparison to the keels 450, 426 ofFIGS. 28-30. The relative shortness of the keels 550, 560 may aid suchkeels in following the openings 470, 472, respectively. In addition, theshortness of the keels 550, 560 and the ease with which such keelsfollow the openings 470, 472, respectively, allows the keels to beconfigured as either straight or curved keels, which increases thedesign options of the prosthetic joint 410. The keels 550, 560 may alsobe tapered to assist in insertion of the keels into the upper and lowervertebrae V_(U), V_(L).

[0179] IV. Anterior-Oblique Prosthetic Joint

[0180] Another approach that can be used to avoid potential damage toimportant anatomical structures such as nerve roots, dura, ligamentumflavum and interspinous ligament is the anterior oblique approach. Forexample, the straight anterior approach to the disc space betweenvertebra L4 and L5, as well as the superior disc levels, can presenthigh surgical risks during the insertion of a total disc replacementimplant because of the attachment of the major vessels to the anterioraspect of the spine.

[0181] Referring to FIGS. 39-41, shown therein is an intervertebralarticulating prosthetic joint 600 according to another form of thepresent disclosure. The prosthetic joint 600 extends generally along alongitudinal axis L and includes a first articular component 602 and asecond articular component 604. The articular components 602, 604cooperate to form the prosthetic joint 600 which is sized and configuredfor disposition within an intervertebral space between adjacentvertebral bodies.

[0182] The prosthetic joint 600 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies to maintain or restoremotion substantially similar to the normal bio-mechanical motionprovided by a natural intervertebral disc. More specifically, thearticular components 602, 604 are permitted to pivot relative to oneanother about a number of axes, including lateral or side-to-sidepivotal movement about longitudinal axis L and anterior-posteriorpivotal movement about a transverse axis T. It should be understood thatin a preferred embodiment, the articular components 602, 604 arepermitted to pivot relative to one another about any axes that lies in aplane that intersects longitudinal axis L and transverse axis T.Additionally, the articular components 602, 604 may be permitted torotate relative to one another about a rotational axis R. Although thearticulating joint 600 has been illustrated and described as providing aspecific combination of articulating motion, it should be understoodthat other combinations of articulating movement are also possible andare contemplated as falling within the scope of the present disclosure.It should also be understood that other types of articulating movementare also contemplated, such as, for example, relative translational orlinear motion.

[0183] Although the articular components 602, 604 of prosthetic joint600 may be formed from a wide variety of materials, in one embodiment,the articular components 602, 604 are formed of acobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However,in alternative embodiments of the invention, the articular components602, 604 may be formed of other materials such as titanium or stainlesssteel, a polymeric material such as polyethylene, or any otherbiocompatible material that would be apparent to one of ordinary skillin the art. The surfaces of the articular components 602, 604 that arepositioned in direct contact with vertebral bone are preferably coatedwith a bone-growth promoting substance, such as, for example, ahydroxyapatite coating formed of calcium phosphate. Additionally, thesurface of the articular components 602, 604 that are positioned indirect contact with vertebral bone are preferably roughened prior tobeing coated with the bone-growth promoting substance to further enhancebone on-growth. Such surface roughening may be accomplished by way of,for example, acid etching, knurling, application of a bead coating, orother methods of roughening that would occur to one of ordinary skill inthe art.

[0184] Articular component 602 includes a support plate 610 having anarticular surface 612 and an opposite bearing surface 614. Support plate610 may be sized and shaped to substantially correspond to the size andshape of the vertebral endplate of an adjacent vertebra. In oneembodiment, the support plate 610 is shaped in a triangular-likeconfiguration to facilitate an oblique insertion approach from eitherthe left or right side of the spine, and as such, includes side portionsP1, P2 and P3. The side portions P1, P2 and P3 may take a variety ofconfigurations including curved (illustrated by P2) or straight(illustrated by P1 and P3) configurations.

[0185] The support plate 610 can include one or more notches 616 orother types of indicia for receiving and engaging with a correspondingportion of a surgical instrument (also not shown) to aid in themanipulation and insertion of the prosthetic joint 600 within anintervertebral space between adjacent vertebrae. The surgical instrument(not shown) is preferably configured to hold the articular components602, 604 at a predetermined orientation and spatial relationshiprelative to one another during manipulation and insertion of theprosthetic joint 600, and to release the articular components 602, 604once properly positioned between the adjacent vertebrae.

[0186] In one embodiment, the articular surface 612 includes aprojection 620 having a convex shape, which may be configured as aspherical-shaped ball (half of which is shown). It should be understoodthat other configurations of the projection 620 are also contemplated,such as, for example, cylindrical, elliptical or other arcuateconfigurations or possibly non-arcuate configurations. It should also beunderstood that the remaining portion of articular surface 612 may takeon planar or non-planar configurations, such as, for example, an angularor conical configuration extending about the projection 620.

[0187] A flange member or keel 640 extends from the bearing surface 614and is configured for disposition within a preformed opening in theadjacent vertebral endplate. In one embodiment, the keel 640 extendsperpendicularly from the bearing surface 614 and is approximatelycentrally located along the bearing surface 614. However, it should beunderstood that other positions and orientations of the keel 640 arealso contemplated. Furthermore, more keels 640 can be used, for similaror additional reasons.

[0188] In one embodiment, the keel 640 extends along a substantialportion of the support plate 610. The keel 640 is straight, but extendsalong a direction towards the notches 616 and is parallel with one ofthe side portions P1 of the support plate 610. In the present example,the keel 640 is positioned between the transverse axis T and lateralaxis L. Such an embodiment accommodates insertion of the prostheticjoint 600 using an oblique approach as opposed to the anterior, lateral,or transforaminal approaches discussed above. In a further embodiment,the keel 640 may be angled, tapered, or configured in some other shapeto facilitate the functional demands of the keel. In still anotherembodiment, the keel 640 may be configured as a winged keel, including atransverse portion (not shown) extending across the main body portion ofkeel 640.

[0189] The keel 640 also includes a pair of openings 646 extendingtherethrough to facilitate bone through-growth to enhance fixation tothe adjacent vertebra. Additionally, a gap 648 may also be formed in thekeel 640 to further facilitate bone through-growth. The gap 648 alsoprovides a reference point such that an X-ray can be used to evaluatethe positioning and alignment of the support plate 602 during insertionof the prosthetic joint 600. It should be understood that any number ofopenings 646 or gaps 648 may be defined through keel 640, including asingle opening or gap or several openings and gaps. It should also beunderstood that the openings 646 and gap 648 need not necessarily extendentirely through the keel 640, but may alternatively extend partiallytherethrough. It should further be understood that the keel 640 need notnecessarily define any openings 646 or gaps 648 extending eitherpartially or entirely therethrough. Additionally, although the openings646 are illustrated as having a circular configuration, it should beunderstood that other sizes and configurations of openings 646 are alsocontemplated. As discussed above, the surfaces of the articularcomponent 602 that are in direct contact with vertebral bone may becoated with a bone-growth promoting substance. Specifically, the bearingsurface 614 and the surfaces of the keel 640 can be coated withhydroxyapatite to promote bony engagement with the adjacent vertebrae.As also discussed above, the bearing surface 614 and the surfaces ofkeel 640 can be roughened prior to application of the hydroxyapatitecoating.

[0190] In one embodiment, the articular component 604 includes a supportplate 650 having an articular surface 652 and an opposite bearingsurface 654. Support plate 650 may be sized and shaped to substantiallycorrespond to the size and shape of the vertebral endplate of anadjacent vertebra. In one embodiment, the support plate 610 is shaped ina triangular-like configuration to facilitate an oblique insertionapproach from either the left or right side of the spine, and as such,includes side portions P4, P5 and P6. The side portions P4, P5 and P6may take a variety of configurations including curved (illustrated byP5) or straight (illustrated by P4 and P6) configurations. The supportplate 650 can include one or more notches 656 or other types of indiciafor receiving and engaging with a corresponding portion of a surgicalinstrument, such as discussed above with reference to articularcomponent 602.

[0191] In one embodiment, the articular surface 652 includes a recess660 having a convex shape, which may be configured as a spherical-shapedsocket. However, it should be understood that other configurations ofthe recess 660 are also contemplated, such as, for example, cylindrical,elliptical or other arcuate configurations or possibly non-arcuateconfigurations. The remaining portion of the articular surface 652 canbe angled or otherwise configured to facilitate the insertion and/or useof the prosthesis.

[0192] Although the concave recess 660 is illustrated as having agenerally smooth, uninterrupted articular surface, it should beunderstood that a surface depression or cavity may be defined along aportion of the recess 660 to provide a means for clearing out matter,such as particulate debris, that is disposed between the abuttingarticular surfaces of components 602, 604. In such case, the convexarticular surface of the ball 620 may alternatively define a generallysmooth, uninterrupted articular surface. In another embodiment of theinvention, each of the convex projection 620 and the concave recess 660may define a surface depression to facilitate removal of particulatematter disposed between the abutting articular surfaces.

[0193] A flange member or keel 670, configured similar to the keel 640of articular component 602, extends from the bearing surface 654. In oneembodiment, the keel 670 can be centrally located, and is positioneddirectly or parallel in-line with the keel 640. The keel 640 isstraight, but extends along a direction towards the notches 656 and isparallel with one of the side portions P4 of the support plate 650. Suchan embodiment accommodates insertion of the prosthetic joint 600 usingan oblique approach as opposed to the anterior, lateral, ortransforaminal approaches discussed above. In some embodiments, theposition of the keel 670 can be offset to help circumvent veins,arteries, bony portions, or other obstacles that may be in place duringthe insertion of the joint 600.

[0194] It should be further understood that other positions, shapes,orientations, and quantities of the keel 670 are also contemplated. Itshould also be understood that more keels 670 can be used, for similaror additional reasons. Also, the keel 670 may be angled, tapered, orconfigured in some other shape to facilitate the functional demands ofthe keel. In still another embodiment, the keel 670 may be configured asa winged keel, including a transverse portion (not shown) extendingacross the main body portion of keel 670.

[0195] In one embodiment, the keel 670 also includes a pair of openings676 extending therethrough to facilitate bone through-growth to enhancefixation to the adjacent vertebra. Additionally; a gap 678 may also beformed in the keel 670 to further facilitate bone through-growth. Thegap 678 also provides a reference point such that an X-ray can be usedto evaluate the positioning and alignment of the support plate 604during insertion of the prosthetic joint 600. It should be understoodthat any number of openings 676 or gaps 678 may be defined through keel670, including a single opening or gap or several openings or gaps. Itshould also be understood that the openings 676 and gap 678 need notnecessarily extend entirely through the keel 670, but may alternativelyextend partially therethrough. It should further be understood that thekeel 670 need not necessarily define any openings 676 or gaps 678extending either partially or entirely therethrough; Additionally,although the openings 676 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 676 are also contemplated. As discussedabove, the surfaces of the articular component 602 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 654 and thesurfaces of the keel 670 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 654 and the surfaces of keel 670 can be roughenedprior to application of the hydroxyapatite coating.

[0196] In some embodiments, one or both of the keels 640, 670 mayinclude a sharp forward edge, illustrated by edges 680, 682. By havingsuch an edge, insertion of the keels 640, 670 into the associatedvertebral body is facilitated. Also, the edges 680, 682 can be ofsufficient sharpness that the vertebral body does not require a slot forreceiving the keel 640, 670, discussed in greater detail below.

[0197] Referring to FIGS. 42-44 a, to accommodate insertion of theprosthetic joint 600 within the intervertebral space, the upper andlower vertebrae V_(U), V_(L) can be prepared to accept the prostheticjoint 600 therebetween. Referring specifically to FIG. 43, for theconfiguration of the prosthetic joint 600 of FIGS. 38-40, multiple slots690, 692 are formed along the vertebral endplates of the lower vertebraeV_(L) and the upper vertebrae V_(U), respectively. The slots 690, 692can be created by the keels 640, 670 themselves, or can be preparedbeforehand by one or more of the methods discussed above. It can be seenfrom FIGS. 42-44, that if one or more vessels 694 are obstructing astraight anterior approach, the oblique approach will allow for ananterior/lateral insertion. The implant 600 design also ensures asufficient contact surface for contacting the bony endplates of thevertebrae V_(U), V_(L).

[0198] Referring to FIG. 44b, in one embodiment, the prosthetic joint600 can be inserted into the intervertebral space via instrumentationsuch as the 4-in-1 guide as disclosed in co-pending application U.S.Ser. No. 10/430,473, which is herein incorporated by reference. In oneexample of an insertion process for inserting the prosthetic joint 600,the midline M of the vertebrae V_(U), V_(L) is located using imagingequipment and a pin 695 is inserted into the upper vertebra V_(U) alongthe midline. An oblique guide member 696 is then connected to the pin695 via a flange 697 and a handle (not shown) associated with theoblique guide member 696 is then adjusted to a proper position. Anoblique pin 698 of the oblique guide member 696 is then impacted intothe upper vertebra V_(U) to fix the oblique guide member, therebyindicating the entering reference point and the direction of implantinsertion for the prosthetic joint 600. The 4-in-1 guide (not shown) canthen be used to implant the prosthetic joint 600 into the intervertebralspace from an anterior-oblique approach, the details of which are morefully discussed in co-pending application U.S. Ser. No. 10/430,473.

[0199] V. Mobile-Bearing Prosthetic Joint

[0200] In another embodiment, the above-described prosthetic joints canbe modified to provide for translational movement as well as rotationalmovement. For example, referring to FIGS. 45-47, a mobile-bearingprosthetic joint for anterior insertion is generally referred to byreference numeral 700. It is understood that the mobile-bearingprosthetic joint 700 is described with respect to anterior insertion forthe sake of clarity only, and therefore, a variety of insertiondirections are contemplated for the mobile-bearing prosthetic joint.

[0201] The prosthetic joint 700 extends generally along a longitudinalaxis L and includes a first articular component 702 and a secondarticular component 704. The articular components 702, 704 cooperate toform the prosthetic joint 700 which is sized and configured fordisposition within an intervertebral space between a pair of vertebralbodies, such as an intervertebral space S1 between adjacent vertebralbodies V_(S), V_(I) (FIG. 48).

[0202] The prosthetic joint 700 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies V_(S), V_(I) to maintainor restore motion substantially similar to the normal bio-mechanicalmotion provided by a natural intervertebral disc but with the addedelement of translational motion. More specifically, the articularcomponents 702, 704 are permitted to pivot relative to one another abouta number of axes, including lateral or side-to-side pivotal movementabout a longitudinal axis L and anterior-posterior pivotal movementabout a transverse axis T. It should be understood that in oneembodiment, the articular components 702, 704 are permitted to pivotrelative to one another about any axes that lies in a plane thatintersects longitudinal axis L and transverse axis T. Additionally, thearticular components 702, 704 are permitted to rotate relative to oneanother about a rotational axis R. In addition, the articular components702, 704 are permitted to translate relative to one another as will befurther described.

[0203] Although the articular components 702, 704 of prosthetic joint700 may be formed from a wide variety of materials, in one embodiment,the articular components 702, 704 are formed of acobalt-chrome-molybdenum metallic alloy (ASTM F-799 or-F-75). However,in alternative embodiments, the articular components 702, 704 may beformed of other materials such as titanium or stainless steel, apolymeric material such as polyethylene, or any other biocompatiblematerial that would be apparent to one of ordinary skill in the art. Thesurfaces of the articular components 702, 704 that are positioned indirect contact with vertebral bone may be coated with a bone-growthpromoting substance, such as, for example, a hydroxyapatite coatingformed of calcium phosphate. Additionally, the surface of the articularcomponents 702, 704 that are positioned in direct contact with vertebralbone may be roughened prior to being coated with the bone-growthpromoting substance to further enhance bone on-growth. Such surfaceroughening may be accomplished by way of, for example, acid etching,knurling, application of a bead coating, or other methods of rougheningthat would occur to one of ordinary skill in the art.

[0204] Articular component 702 includes a support plate 706 having anarticular surface 708 and an opposite bearing surface 710. Support plate706 may be sized and shaped to substantially correspond to the size andshape of the vertebral endplate of an adjacent vertebra. The supportplate 706 can include one or more notches 712 or other types of indiciafor receiving and engaging with a corresponding portion of a surgicalinstrument (not shown) to aid in the manipulation and insertion of thearticulating joint 700 within an intervertebral space between adjacentvertebrae. The surgical instrument (not shown) is preferably configuredto hold the articular components 702, 704 at a predetermined orientationand spatial relationship relative to one another during manipulation andinsertion of the articulating joint 700, and to release the articularcomponents 702, 704 once properly positioned between the adjacentvertebrae.

[0205] In one embodiment, and referring to FIGS. 49a and 49 b, a recess714 is formed in the articular surface 708. A circumferential edge 716defining the recess 714 along the articular surface 708 is in aconcentric relationship with a recess surface 718, yet has a smallerdiameter relative to the recess surface due to a diverging circular side720 (FIG. 48b) of the recess 714. Although described with reference tohaving a circular shape, it is understood-that the recess 714 may takeany number of shapes such as square, triangular, or rectangular shapes.

[0206] Referring to FIGS. 50a and 50 b, the recess 714 (FIG. 49b) isdesigned to receive a portion of a modular projection member 722. Theprojection member 722 includes a flange portion 724, which is shaped tocorrespond to the shape of the recess 714. As such, the flange portion724 includes a diverging circumferential side 726, which terminates at asubstantially planar engagement surface 728. The engagement surface 728is adapted to engage the substantially planar recess surface 718 (FIG.49b). It is understood, however, that although depicted as beingsubstantially planar, the engagement surface 728 and the recess surface718 may take any number of corresponding shapes. The diameter of theengagement surface 728 is smaller than the diameter of the recesssurface 718, thereby allowing translation of the modular projectionmember 722 relative to the articular component 702.

[0207] The remaining portion of the modular projection member 722 isdefined by a projection 730 having a convex shape, which may beconfigured as a spherical-shaped ball (half of which is shown). Itshould be understood that other configurations of the projection 730 arealso contemplated, such as, for example, cylindrical, elliptical orother arcuate configurations or possibly non-arcuate configurations. Itshould also be understood that the remaining portion of articularsurface 708 may take on planar or non-planar configurations, such as,for example, an angular or conical configuration extending about theprojection 224.

[0208] In one embodiment, the convex articular surface of the projection730 is interrupted by a surface depression or cavity 732 extending alongthe projection 730. In one embodiment, the surface depression 732 isconfigured as a groove. However, it should be understood that othertypes of surface depressions are also contemplated, including nodepression at all. One purpose of the groove 732 is to facilitate theremoval of matter disposed between abutting portions of the articularcomponents 702, 704. More specifically, the groove 732 may aid inclearing out matter such as, for example, particulate material, that isdisposed between the abutting articular surfaces of components 702, 704.

[0209] Referring to FIGS. 45 and 49b, a flange member or keel 740extends from the bearing surface 710 and is configured for dispositionwithin a preformed opening in the adjacent vertebral endplate (such asV_(I) in FIG. 47). In one embodiment, the keel 740 extendsperpendicularly from the bearing surface 710 and is approximatelycentrally located along the bearing surface 710. However, it should beunderstood that other positions and orientations of the keel 740 arealso contemplated.

[0210] In one embodiment, the keel 740 extends along substantially theentire length of the support plate 706. Such an embodiment wouldaccommodate insertion of the articulating joint 700 using an anteriorapproach. However, as discussed above, other approaches such as lateral,transforaminal, and anterior-oblique approaches are also contemplatedfor insertion of the prosthetic joint 700. In a further embodiment, thekeel 740 may be angled, tapered, or configured in some other shape tofacilitate the functional demands of the keel. In still anotherembodiment, the keel 740 may be configured as a winged keel, including atransverse portion (not shown) extending across the main body portion ofkeel 740.

[0211] The keel 740 also includes a pair of openings 742 extendingtherethrough to facilitate bone through-growth to enhance fixation tothe adjacent vertebra. However, it should be understood that any numberof openings 742 may be defined through keel 740, including a singleopening or three or more openings. It should also be understood that theopenings 742 need not necessarily extend entirely through the keel 740,but may alternatively extend partially therethrough. It should furtherbe understood that the keel 740 need not necessarily define any openings742 extending either partially or entirely therethrough. Additionally,although the openings 742 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of the openings 742 are also contemplated. As discussedabove, the surfaces of the articular component 702 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 710 and thesurfaces of the keel 740 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 710 and the surfaces of keel 740 can be roughenedprior to application of the hydroxyapatite coating.

[0212] Referring to FIGS. 45-47, in one embodiment, the articularcomponent 704 includes a support plate 750 having an articular surface752 and an opposite bearing surface 754. Support plate 750 may be sizedand shaped to substantially correspond to the size and shape of thevertebral endplate of an adjacent vertebra. The support plate 750 caninclude one or more notches 756 or other types of indicia for receivingand engaging with a corresponding portion of a surgical instrument, suchas discussed above with reference to articular component 702.

[0213] In one embodiment, the articular surface 752 includes a recess758 (FIG. 47), which has a convex shape, such as that of aspherical-shaped socket. However, it should be understood that otherconfigurations of the recess 758 are also contemplated, such as, forexample, cylindrical, elliptical or other arcuate configurations orpossibly non-arcuate configurations. The remaining portion of thearticular surface 752 can be angled or otherwise configured tofacilitate the insertion and/or use of the articulating joint 700.

[0214] Although the concave recess 758 is illustrated as having agenerally smooth, uninterrupted articular surface, it should beunderstood that a surface depression or cavity may be defined along aportion of the recess 758 to aid in clearing out matter, such asparticulate debris, that is disposed between the abutting articularsurfaces of articular components 702, 704. In such case, the convexarticular surface of the projection 730 may alternatively define agenerally smooth, uninterrupted articular surface. In anotherembodiment, each of the convex projection 730 and the concave recess 758may define a surface depression to facilitate removal of particulatematter disposed between the abutting articular surfaces.

[0215] A flange member or keel 760, configured similar to the keel 740of articular component 702, extends from the bearing surface 754. In oneembodiment, the keel 760 extends perpendicularly from the bearingsurface 754 and is approximately centrally located along bearing surface754. However, it should be understood that other positions andorientations of the keel 760 are also contemplated. It should also beunderstood that the articular component 704 may include two or morekeels 760 extending from the bearing surface 754.

[0216] In one embodiment, the keel 760 extends along substantially theentire length of the support plate 750. Such an embodiment wouldaccommodate insertion of the prosthetic joint 700 using an anteriorapproach. However, as discussed above, other approaches such as lateral,transforaminal, and anterior-oblique approaches are also contemplatedfor insertion of the prosthetic joint 700. In a further embodiment, thekeel 760 may be angled, tapered, or configured in some other shape tofacilitate the functional demands of the keel. In still anotherembodiment, the keel 760 may be configured as a winged keel, including atransverse portion (not shown) extending across the main body portion ofkeel 760.

[0217] The keel 760 also includes a pair of openings 762 extendingtherethrough to facilitate bone through-growth to enhance fixation tothe adjacent vertebra. However, it should be understood that any numberof openings 762 may be defined through keel 760, including a singleopening or three or more openings. It should also be understood that theopenings 762 need not necessarily extend entirely through the keel 760,but may alternatively extend partially therethrough. It should furtherbe understood that the keel 760 need not necessarily define any openings762 extending either partially or entirely therethrough. Additionally,although the openings 762 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 762 are also contemplated. As discussedabove, the surfaces of the articular component 704 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 754 and thesurfaces of the keel 760 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 754 and the surfaces of keel 760 can be roughenedprior to application of the hydroxyapatite coating.

[0218] In some embodiments, one or both of the keels 740, 760 mayinclude a sharp forward edge, illustrated by edge 760 a of FIGS. 45 and46. By having such an edge, insertion of the keel 740, 760 into theassociated vertebral body is facilitated. Also, the edge 760 a can be ofsufficient sharpness that the vertebral body does not require a slot forreceiving the keel 760, discussed in greater detail below.

[0219] Referring to FIG. 45, the mobile-bearing prosthetic joint 700 isassembled by inserting the modular projection 722 member into the recess714 formed in the articular surface 708 of articular component 702. Uponassemblage, the prosthetic joint 700 is ready to be inserted into thedisc space S1 between adjacent vertebral bodies V_(S), V_(I) (FIG. 48).

[0220] Referring to FIG. 48, to accommodate insertion of the prostheticjoint 700 within the intervertebral space S1, the adjacent vertebralbodies V_(S), V_(I) can be prepared to accept the prosthetic joint 700therebetween. For the configuration of the prosthetic joint 700 of FIGS.45-47, slots 770, 772 are formed along the vertebral endplates of thevertebrae V_(S) and the vertebrae V_(I), respectively. The slots 770,772 can be created by the keels 740, 760 themselves, or can be preparedbeforehand by one or more of the methods discussed above.

[0221] Upon insertion into the disc space S1, the prosthetic joint 700allows translational movement of the articular component 704 relative tothe articular component 702 due to the engagement of the modularprojection 722 with the concave recess 758 of articular component 704.For example, in FIG. 51, the modular projection member 722 is shown in aposterior position (which would result in movement of the articularcomponent 704 in the posterior direction P), while in FIG. 52, themodular projection member 722 is shown in an anterior position (whichwould result in movement of the articular component 704 in the anteriordirection A). FIGS. 51 and 52 are of course only exemplary of thetranslational movement allowed by the implementation of modularprojection member 722 and the corresponding recess 714, and thus, theamount of translational movement of the modular projection member 722,and therefore the articular component 704, relative to the articularcomponent 702 can vary, including in directions other than P and A.

[0222] Furthermore, the positioning of the modular projection member 722within the recess 714 of the articular component 702 allows the modularprojection to spin relative to the articular component 702. Thus, insuch an embodiment, the modular projection member 722 adds the benefitof being able to impart rotation to the articular component 704 (via theengagement with the recess 758) independent of translational movementimparted to the articular component 704. Such independent relationshipbetween translational and rotational movement adds to the amount ofmobility experienced at the prosthetic joint 700 relative to prostheticjoints for which translational movement is dependent upon rotationalmovement and vice versa.

[0223] The present disclosure has been described relative to severalpreferred embodiments. Improvements or modifications that becomeapparent to persons of ordinary skill in the art after reading thisdisclosure are deemed within the spirit and scope of the application.For example, the articulating components of the above-describedarticulating joints may be reversed without departing from certainaspects of the disclosure. Accordingly, it is understood that severalmodifications, changes and substitutions are intended in the foregoingdisclosure and, in some instances, some features of the disclosure willbe employed without a corresponding use of other features. It is alsounderstood that all spatial references, such as “longitudinal” and“transverse,” are for illustrative purposes only and can be variedwithin the scope of the disclosure. Accordingly, it is appropriate thatthe appended claims be construed broadly and in a manner consistent withthe scope of the disclosure.

What is claimed is:
 1. A system for simultaneously removing portions ofproximate endplates of adjacent vertebral bodies, the system comprising:a guide member defining an extended opening extending therein, the guidemember being configured to fit in a disc space between the two vertebralbodies; a bit member positioned within the opening of the guide member,the bit member including a superior cutting portion for cutting the endplate of a superior vertebral body, and an inferior cutting portion forcutting the end plate of an inferior vertebral body; a rotatable elementoperatively connected to the bit member to impart rotational movement tothe superior and inferior cutting portions, and operatively connected tothe guide member for moving the bit member along at least a portion ofthe extended opening.
 2. An instrument for cutting a path in bone,comprising a non-linear guide member defining a non-linear openingextending therein, and a bit member positioned within the opening of theguide member, the bit member being adapted to move within the opening ofthe guide member to cut a path in bone.
 3. The instrument of claim 2wherein the bit member comprises at least one bearing assembly disposedadjacent to the guide member to accommodate positioning of the bitmember within the opening of the guide member.
 4. The instrument ofclaim 2 further comprising at least one rotatable element to accommodaterotational movement of the bit member within the opening of the guidemember.
 5. The instrument of claim 4 wherein the rotatable element is agear assembly.
 6. The instrument of claim 2 wherein the bit memberextends from a first vertebra to an adjacent second vertebra.
 7. Theinstrument of claim 4 further comprising a power source operativelyconnected to the rotatable element of the bit member for impartingrotational movement to the bit member.
 8. The instrument of claim 7further comprising a conduit extending from the guide member for housinga shaft associated with the power source and the rotatable element. 9.The instrument of claim 8 wherein the conduit is operatively connectedto the bit member and is adapted to impart translational movement to thebit member.
 10. The instrument of claim 2 wherein the non-linear guidemember provides a relatively smooth curvature and a degree of curvatureof the curved guide member corresponds to a predetermined cutting path.11. The instrument of claim 10 wherein the predetermined cutting pathaccommodates a transforaminal approach for cutting vertebral bone. 12.The instrument of claim 2 wherein non-linear guide member provides arelatively smooth curvature and a degree of curvature of the guidemember is variable.
 13. The instrument of claim 8 further comprising ahandle connected to the guide member.
 14. The instrument of claim 13wherein the handle is disposed concentrically about the conduit.
 15. Aninstrument for cutting a path in bone, comprising a curved guide memberdefining a curved opening extending therein, a bit member positionedwithin the opening of the guide member, a rotatable element operativelyconnected to the bit member to impart rotational movement to the bitmember, a handle operatively connected to the bit member to imparttranslational movement to the bit member, wherein the bit member isadapted to cut a curved path into bone via rotational movement in andtranslational movement through the guide member.
 16. The instrument ofclaim 15 wherein the curved path cut into bone corresponds to atransforaminal approach to the bone.
 17. The instrument of claim 15further comprising at least one bearing assembly to accommodatepositioning of the bit member within the curved opening of the guidemember.
 18. The instrument of claim 15 wherein the degree of curvatureof the guide member is variable to correspond to a predetermined cuttingpath.
 19. A method for cutting a curved path into bone, comprisingproviding an instrument having a curved guide member, the curved guidemember defining a curved opening therein, positioning a bit memberwithin the opening of the guide member, actuating the instrument toimpart rotational movement to the bit member, engaging the bit memberwith bone, and imparting a translational force to the bit member to cuta curved path in bone.
 20. The method of claim 19 wherein the curvedcutting path is variable.
 21. The method of claim 18 wherein actuatingthe instrument imparts rotational movement to the bit member via a gearassembly.
 22. The method of claim 18 wherein actuating the instrumentimparts rotational movement to the bit member via a pneumatic system.